wet in wet
Wet in wet (or wet into wet, with-or-without the useless hyphens) refers to any passage where wet paint is applied to wet paper, or where wet paint or water is added into or on top of wet paint already on the paper a huge range of possible combinations.
The soft, flowing, complex or random effects possible with wet in wet techniques are the unique signature of the watercolor medium. Even acrylics, though they can be diluted into glazes or slopped around in watery patterns, can't match the expressive textures of diffusion, backrun, pigment granulation and color gradation possible with a watery gum arabic vehicle on paper.
Wash applications had been used in ink or watercolor drawings since the middle 18th century, but wet in wet effects were innovated in the early 1800's and systematically exploited by the English painter J.M.W. Turner. He became famous for using diffuse color areas, created by mixtures on the paper of red, yellow and blue pigments, to establish the dominant value shapes in landscape paintings, and for using a variety of wet in wet textures to represent clouds, mists, reflections in water, and the like.
Turner's innovations were extended by several Victorian rivals and admirers, though for different ends. Alfred William Hunt used wet in wet methods with greater realism and control, while Hercules Brabazon Brabazon developed them toward greater lyrical spontaneity. Today, wet in wet effects are usually associated with the populist style of the California Scene Painters of the 1930's and the sloshy, lossy workshop style of Edgar Whitney and his many students (Frank Webb, Tony Couch and Barbara Nechis among them). Even a hardnosed technician like Gerhard Richter uses wet in wet methods to achieve complex and unique visual textures.
All these artists are masters at managing the marriage of paint and water to create remarkable evocations of light and atmosphere. Wet in wet techniques are especially well suited to landscape painting, because the broad, dynamic, irregular and uncontrolled paint shapes resemble the large, energetic, irregular and chaotic forms of nature. When wet in wet is used in nonrepresentational painting, the style usually has its roots in a landscape esthetic rather than the human figure.
Wet in wet also has a long history as a teaching aid. Students must give up their anxieties for control and accuracy when the paint is applied to wet paper; the unpredictability of wet in wet effects teaches them to improvise with the paint behavior rather than try to dominate it.
Artists today tend to disparage painting styles associated with the overt display of sentiment, amateur painting or commercial design. (Before his workshop career, Whitney was an advertising artist and painted the cover illustrations for many paperback detective novels.) Watercolor painters today minimize wet in wet effects in the opinion they are too uncontrollable, "precious" or passé for serious painting.
In hindsight, it's obvious that wet in wet was and is used to excess by American watercolorists, especially by the "workshop mafia" catering to amateur painters. But you haven't really experienced watercolor painting until you have taken the plunge into wet in wet techniques.
the balancing act
At the outset we need a fundamentally simple idea of how wet in wet painting works, a single concept that can pull together every detail of the process. Remarkably, this is hard to find.
For the typical point of view, here are some observations by Jean-Louis Morelle, a French watercolorist known for his use of wet in wet effects, taken from the preface to his Aquarelle: L'Eau Créatice (2002):
Throughout the years that I have practised watercolor painting, one thing has become clear: before it becomes paint, watercolor is first and foremost water. Water fills us with fear and pleasure in equal measure, making us realize the rich and ambivalent relationship that we have always had with this element.... I have seen these feelings re-emerge in many amateur painters nobody is truly free of them. This gave me the idea to develop a method of teaching based on in-depth observation of the phenomena that water creates. Very simple conclusions are born from such observation. We very quickly notice that we have no control over water and that we cannot force it to do anything. We must respect it. Firstly it spreads, next it is absorbed and then it dries after a period of time.
I agree with everything Morelle says in his opening statement, but I disagree with everything he says in the text in red.
Every watercolor book I have encountered suffers from the urge to reduce wet in wet painting to "very simple conclusions." These solutions take two forms: either the author calls the process "random," "unpredictable" or "uncontrollable"; or he caricatures it "it spreads, is absorbed and then dries" in a way that provides little insight. Morelle does both.
In fact, all wet in wet effects result from an imbalance of wetness between paper, brush and fresh paint:
Paper wetness. Paper is wet in two different dimensions: surface moisture and core or inner moisture. Surface moisture primarily affects the behavior of the paint. Inner moisture adds to the wetness of the surface moisture, and increases the time it takes the paper to dry from evaporation.
Brush wetness. The wetness of the brush is the amount liquid it can release over a given area of already wet paper. This depends on the brush capacity (tuft size and type of hair or bristle), the charge (how much water it contains), the release (the speed, angle and pressure of your brushstroke), and the amount of water already on the paper (the brush/paper balance). These points are discussed in the page on the brush and brushstrokes.
Paint wetness (dilution). Paint dilution affects the thickness or viscosity of the paint, which determines how much liquid will release from the brush (the paint/brush balance) and how rapidly the paint will diffuse or expand on wet paper (the paint/paper balance).
It is your awareness of this three way moisture balance, and your ability to adjust exactly the balance of moisture in paper, brush and paint, that determines your control over the outcomes of wet in wet painting.
the three sided balance of wet in wet painting
You must achieve three goals in order to master wet in wet effects. (1) Learn the distinct gradations in paper wetness, brush wetness, and paint wetness (dilution); (2) learn how to recognize and adjust each of these separate wetness levels at will; and (3) learn the visual results that are produced by the combinations of all three.
In these combinations, paint wetness vs. paper wetness is usually the deciding factor, because together these produce the greatest dynamic energy in the behavior of paint on paper, and both influence the relative amount of release (wetness) that is possible with different kinds of brushes.
So it is quite inaccurate to say that "we have no control over water and ... cannot force it to do anything." On the contrary! It is possible and it is within your ability to control water and make it do exactly what you want.
Part of that control lies in limiting water's freedom of action through your choice of paint pigment, paint dilution, brush, brush wetness, paper wetness, paper tilt, and so on controlling wetness through your selection of tools and materials. But the main source of control is turning water against itself, using moisture to guide and control moisture in much the way that forestry workers use fire to control and extinguish a forest fire. This is the wet in wet balancing act.
flow, backrun & diffusion
Before you can begin to study the wetness balance among paper, paint and brush, you must understand the different ways water and paint behave in wet in wet painting techniques.
There is a beautifully simple principle that explains everything about wet in wet painting: water seeks equilibrium of level, distribution and purity. All wet in wet effects (other than the pigment texturing produced by granulation or floccuation) arise from three equilibrium mechanisms acting through water or liquid paint: surface flow, backrun, and diffusion. These mechanisms can occur at the same time or in any combination, though one usually dominates the others. Wet in wet painting is the process of creating a specific wetness imbalance under just the right conditions to cause water to restore its natural balance through the flow, backrun or diffusion you want to occur.
1. Flow. The first mechanism, which restores a uniform level to the water, is gravity flow. This occurs when the water surface itself forms a gradient and water is pulled by gravity from a higher to a lower location. The rule here is:
high into low
meaning that water will tend to flow toward the lowest point of the paper surface. Flow can occur in two ways: when the entire support is tilted or curved so that there is a gradient across its surface, or when the surface of the paper cockles or warps to produce wavy undulations or patterns of random dips and humps.
Gravity flow can also happen when the paper is perfectly flat, a process I will call leveling. Water added to a flat and already wet surface will spread out evenly across the wet area, for example when water from a trickling hose expands across an already wet concrete patio. You will see leveling occur when you add a large quantity of water or very diluted paint to an already wet area of a painting; within a few moments the new moisture has expanded to equalize its level with the wetness around it.
Your control over flow depends on paint and/or paper wetness and the angle of surface gradient. Obviously direct control is possible simply by raising one side of the painting surface (paper or stretching board): more tilt means more flow. But flow is only possible if there is excess moisture on the surface of the paper, and flow becomes more extreme and powerful when there is more moisture on the paper the paint is more diluted, and/or the paper is wetted with more liquid.
If the paper is not stretched and is wet to the core (rather than on the surface), then the paper may cockle or warp, producing an up and down waviness on the surface that creates flow that is not easily under your control. In that case, extreme tilt, soaking up the excess moisture with a brush or sponge, painting with more concentrated (less runny) paint, or waiting until the paper has completely dried are your remedies.
2. Backrun. The second mechanism, which restores even distribution of moisture, appears as backruns. These are created by differences in paper wetness, or unevenness in the distribution of moisture on the paper, which arise because the surface has dried unevenly or because you have added fresh paint to areas that are not completely dried. (Backruns have been given many other names in the watercolor painting literature, including blossoms, ozzles, halos, runbacks and watermarks. I like backrun because it describes literally the process at work.) The rule here is:
wet into moist
meaning that areas of more concentrated or greater quantity water or paint will try to flow into already wet areas of less concentrated water or paint, and so make the distribution of the water the same across both areas.
The primary mechanism at work is capillarity, the tendency of water to migrate far into small, hydrophilic or premoistened spaces or interstices, which is how a sponge absorbs water from your kitchen counter. (Most watercolor papers, when dry, inhibit the natural capillary flow of water into the feltlike mat of cellulose fibers by the use of an internal sizing.) Capillary action is distinctive because it can cause water to move higher than the water level, for example upwards on a slightly tilted watercolor paper. Gravity flow cannot go uphill, but if the watercolor paper is flat then leveling can also contribute to the expansive force of a backrun when fresh paint or water is added to an already wet area of the painting.
This process normally does not include "moist into dry", but small backruns can occur from moist into dry areas of porous paper papers that have no inner sizing, little surface sizing, and a coarse, feltlike fiber density (apparent as poor resistance to folding and a muffled, dull rattle like cardboard).
How do you control backruns? Primarily through the balance between paper wetness and paint wetness (dilution and volume of paint), and secondarily through the balance between paper wetness and brush wetness (brush capacity or release).
To enhance backruns, work on paper that is at a satin or moist wetness, lay the paper flat, and increase the amount of moisture added to the painted area by using a larger brush, a fully charged brush, and more diluted paint. To minimize backruns, work on a completely dry or completely wet paper surface, tilt the support slightly, and wick up excess water that collects at the bottom of freshly painted areas. Use a smaller brush, a wicked brush, less paint, or thicker paint.
There is no easy way to stop a backrun once it has started. If the paint is still quite fresh and the backrun has just started, blot the entire area with a paper towel, wait for the paint to completely dry, then repaint. If the paint has already started to dry, tilt the support if possible so that the backrun is moving uphill and wick up excess water from its center not from its edges, as more water simply flows from the center to the edge and the backrun continues its course. Once the backrun has completely dried, you can substantially erase the backrun edge by careful wetting and lifting with a small synthetic flat brush and clean water, blotting as you go with a paper towel.
3. Diffusion. The last mechanism, which restores evenness in the water purity, is diffusion. This is the movement of paint caused by differences in the concentration of solutes in the water. The rule here is:
thick into thin
meaning the thicker concentrations of paint will try to diffuse into thinner concentrations, and any concentration of paint will try to diffuse into pure water. Obviously, diffusion is greatly limited if the paper is only moist or damp.
Diffusion arises from the same mechanism that produces osmosis or osmotic pressure across a permeable barrier. The molecular action necessary to hold pigment particles or carbohydrate (gum) molecules in suspension is literally a weight or pressure on the water, and the water molecules attempt to distribute this weight evenly across a single area of water by spreading out the molecules through diffusion.
Diffusion is affected by the specific gravity (weight in water) and particle size of the paint pigment very small, light pigment particles show much more active diffusion than heavy, large pigment particles which sink quickly to the paper surface. Diffusion is strongly affected by the presence of dispersants, such as ox gall, used to accelerate the wetting (and reduce the milling time) of pigment during paint manufacture. Because small, light pigments are the most difficult to disperse, these are usually also the paints that contain the most added dispersant. So your principal control over diffusion is through choice of paint brand and pigment type.
If we assume pigment attributes are the same, then diffusion depends primarily on the imbalance between paper wetness and paint dilution: diffusion and some pigment texturing are most vivid when a highly concentrated, syrupy to creamy paint is applied to paper at the soaked to shiny stage of wetness. (In contrast, pigment texturing by itself is most vivid in paints at a fluid to watery dilution.)
Diffusion effects will often look like flow effects, with the exception that flow usually creates a subtle parallel streaking of the paint color, or a distinctive "tendril" or branching pattern along the lines of flow, while diffusion tends to produce a slightly irregular feathering along the color boundary. The transition between concentrated and diluted color can also be much more gradual and span a larger area when flow is used.
To summarize: all wet in wet effects arise because of three mechanisms, (1) high into low, (2) wet into moist, and (3) thick (concentrated) into thin (diluted).
The Balance of Forces. Although any of these mechanisms can overwhelm the other two under the right circumstances, there is a fairly consistent ordering or hierarchy in the strength of their combined effects:
flow > backrun > diffusion
That is, in most situations gravity flows can overcome the effects of backrun or diffusion; and where gravity is negligible backruns can reverse the effects of diffusion.
Typically backruns will appear in the same direction as a gravity flow, but in the opposite direction to an expanding diffusion, so watercolor painters become familiar with the antagonism:
diffusion <> backrun
which means that an area of diffusion tends to stimulate a backrun operating against it.
The page on the nature of water describes how these water quirks arise. As a painter your goal is to learn how to recognize and control these various water balancing processes.
The easiest way is to observe the effects within a limited space. For example: tape a sheet of cold pressed or hot pressed (CP, Not or HP) watercolor paper flat on your work table (or use a large watercolor block), and mix up a creamy to fluid dilution of any common paint (ultramarine blue, phthalo green, cadmium orange, quinacridone rose or burnt sienna do nicely). Now use a 1" acrylic flat brush to paint a generous, horizontal stripe of clear water to the left of the paper's center line, and immediately paint a horizontal stripe of paint, just next to and the same size and wetness as the stripe of water, so that the two strokes are separated by only a thin strip of dry paper. Finally, join the two strokes end to end with a single stroke of a small, wet brush across this dry boundary.
The figure below shows what happens when a mixture of phthalo green (PG36) is joined to an area of clear water (a).
diffusion <> backrun
the paper is level and stretched, to eliminate flow
Immediately after the two areas are joined with a single brushstroke, the paint diffuses rapidly into the pure water (b). The quantity of solutes in the paint solution is much greater than in the pure water, so the particles in the more concentrated solution diffuse into the less concentrated (thick into thin). This diffusion slows as the transition from paint mixture to clear water extends over a wider distance the paint becomes more diluted, and the difference between thick and thin becomes less pronounced (c).
At this point most of the clear area has been tinted by paint diffusion, and what used to be clear water is evaporating evenly over its entire surface. Now, however, the painted area begins to dry faster than the area of clear water it contains more paint and therefore less water. This difference in paint wetness causes capillary action to pull the less concentrated solution of paint and water back into the drying painted area (wet into moist), pushing pigment particles along its forward edge as a backrun and leaving a whitened area in its wake (d).
At some point the painted area dries enough so that capillary action can no longer pull more water into it. The backrun stops along a continuous, jagged edge, accented by a dark buildup of compacted pigment particles (e). As the entire swatch dries, many random capillary microcurrents further smooth out the diffused paint in the lefthand area of tinted water, and slightly tighten up the deposit of pigment particles along the boundary of the backrun (f).
Try this simple demonstration with other kinds of paint and other paint dilutions, to see the effect diffusion and backrun have on the process. The example shows what happens when the paper is kept perfectly flat, but you can also try tilting the paper during the diffusion or early backrun stages to see what effect a short interval of flow has on the results.
Edge Quality: The Essence of Wet in Wet. All wet in wet effects occur because of some combination of capillary flow, solute diffusion or gravity flow. So learning to control wet in wet effects means learning to direct the strength, direction and unfolding of those three processes.
However, these processes are important only because they affect a single outcome: edge quality. This means the gradation or transition from one color area to another, the visual shape or texture of the edge, and the visual location or limit of the edge on the paper.
Do not lose sight of this essential point: all wet in wet techniques are used for edge control and nothing else. You can blend colors or produce pigment textures through flow or diffusion, but you can also easily create the same results using other methods. Wet in wet edges can only be produced using wet in wet methods. Therefore it is through the study of edge shaping that you will achieve real mastery and deep understanding of wet in wet techniques.
how wet is the paper?
To get a foothold in your climb to wet in wet mastery, you must start with the single most important factor. And that is in the paper: paper wetness determines all the opportunities and risks in every wet in wet technique.
Paper wetness also brings two specific problems to our attention: (1) how to determine, by looking or touching, the amount of moisture in play, and (2) how to create that level of wetness consistently and at will in any situation. You face the same two problems of moisture recognition and control in your paints and brushes as well, but the problems are most critical and most difficult to master in the paper. Learn how to judge paper wetness, and you'll find brush and paint wetness is much easier to recognize and control.
Paper Wetness. When I began painting in 1996 I could not find a coherent description of paper wetness anywhere. After three years of painting experience, I developed the following six stages of paper wetness, which defines six levels of paper moisture content that have a significant and noticeably different effect on paint behavior, can be easily identified with visual and tactile clues, and can be created at will using explicit techniques. The main points are summarized below.
The tactile (touch) tests necessary to recognize moist and damp paper work best in a moderate ambient temperature and humidity, with no wind. If you are painting outdoors, you must learn to compensate for these environmental distractions. Wind will increase evaporation off the paper surface, drying the paper faster than you expect for a given temperature, but the paper remains wetter than you expect just under the surface. Wind also effaces the sensations of coolness off the paper, making you think the paper is drier than it really is. (The horrible blotches that occur when adding moisture to damp paper were common in my early landscapes!) Unusual heat or direct sun on the paper will warm the water vapor, which erases the coolness cue used to judge moisture. Unusual humidity slows evaporation; unusual cold does the same and also numbs your touch. In general, the safest approach plein air is to allow the paper sufficient time to dry completely, to avoid techniques that require you to judge moist or satin paper, and if you must paint at this wetness, use paints at a higher concentration (a creamy dilution).
Alternative Wetness Systems. This is a good place to mention three wetness description systems that are now available in published sources.
The wetness categories of Gail Speckmann (in Wet-Into-Wet Watercolor, 2001) define levels of paper wetness separately in terms of surface wetness and pulp (inner) wetness. This is an ambitious book, but I feel this method of categorizing paper wetness confuses the issue. As described below, it's the surface wetness that primarily determines the behavior of water and paint. Inner wetness slows down the rate at which paint dries and can make the paper appear drier to sight and touch than it really is. It's easy to mistake the moist or damp stages of wetness for dry paper, and get blotching or backruns in new layers of paint. But I think it is better to visualize this problem as a delay in the drying rate of the paper caused by the inner wetness, and adjust your painting tempo accordingly.
The wetness system of Joseph Zbukvic (in Mastering Atmosphere and Mood in Watercolor, 2002) uses four levels of paper wetness crossed on five levels of paint dilution. This explicitly links the paint wetness (viscosity) to the support wetness, which is a vital point of balance in any painting (see below), but in practice Zbukvic describes the full range of paint dilution only when applied to dry paper, and the effects of creamy or fluid paint dilutions only when applied to paper at shiny or satin wetness.
Finally, I admire Ewa Karpinska's presentation (in Wet-on-Wet Watercolor Painting: A Complete Guide to Techniques and Materials, 2005), not least because her stages of paper wetness correspond closely to my own! She explores effects at three levels of paint dilution pasty (from the tube), creamy, and very diluted using five different painting techniques ("drawing" with the brush using three different amounts of paint, charging wet areas with new paint, and tilting the support). However, two fifths of these wetness/paint/technique combinations are either impractical or labeled "useless" because they are uncontrollable or unsightly, and other combinations are said to produce identical results. So the diversity of techniques is less than it seems. Nevertheless, her book is the best general text on wet in wet that I have seen.
Visualizing Wetness. The ability to accurately judge paper wetness is essential to wet in wet painting technique, and this ability is strengthened if you can visualize what is actually happening on top of and inside the paper. So I've prepared this diagram to help you understand the dynamic relationship between the visual and tactile cues you use to judge paper wetness and the effects of paper wetness on paint. Please study it carefully.
cross section views of six levels of paper wetness
To start, the soaked paper supports a large quantity of excess water on its surface, as you see by comparing the blue area of water to the shaded area of paper. The water is also soaking downward into the paper pulp, and eventually will completely saturate the paper with inner moisture. (The rate of soaking depends on the density and inner sizing of the paper, but typically takes about one minute for every 60 GSM of paper weight, and occurs more quickly in R than in HP papers.) Usually the painter has used a spray bottle, dripping sponge, or large (2" or more) wash brush to apply this much water to the paper.
The total surface water represents far more liquid than can be transferred to the paper by a normal working brush (#12 round or 1" flat), as you see by comparing the area of water to the area of added paint (orange, at right). So the water will completely overwhelm any brushstroke of paint at almost any dilution, which causes the brush to leave ineffectual blobs and contrails of paint on the paper. Flow and diffusion are very powerful and will completely erase all but the largest brushstrokes. Because the surface and interior of the paper are completely saturated with water, pigment particles cannot sink into and securely bond with the paper fibers. As a result, by tilting the paper, nearly all the surface water can be made to sheet off, carrying almost all the fresh paint along with it. Blotting up water with brush or paper towel also takes off most or all of the fresh paint.
The shiny paper is usually also soaked through its inner structure and also has excess water on its surface, but the thickness of the surface layer is less than the up and down variations in the paper surface, so the paper surface texture (in rough R or cold pressed CP sheets, and sometimes the tufts of fiber in HP sheets) is clearly visible. The quantity of surface water is about the same as the quantity of added paint the brush wetness and paper wetness are in balance which means diffusion and flow are still adequate to redistribute the surface moisture, and over short distances with creamy to watery paints flow can be quite active, especially if the paper is tilted slightly or a large brush is used. The reduced moisture means the pigment particles have better contact with the cellulose fibers, and the wet color starts to bond with the paper and will not be completely effaced by flow. Backruns cannot form and brush marks with syrupy to fluid paints remain recognizable, although ddiffusion and leveling flow will cause paint to expand some distance beyond the original brush mark by the time the paper dries. The added paint is usually not sufficient to bring the paper back to a soaked wetness, but it prolongs the shiny wetness in the painted area and replenishes the moisture soaking into the core.
The satin paper contains no excess water on the surface, so flow cannot occur unless creamy to watery paint is used. But there is still surface water, which clings to every bit of surface texture and paper fiber, creating millions of separate tiny reflections that fuse visually into a flat, dull, satiny sheen; this sheen completely effaces the surface texture, making the sheet appear as smooth as satin. The clinging moisture film brings the pigment particles in direct contact with the cellulose fibers, and the wet color has largely bonded with the paper. Usually the paper is soaked through its inner structure: if it is not then the satin wetness will be irregular and blotchy across the surface and will disappear very quickly. The quantity of surface water is now much less than the quantity of added paint, but there is no surface flow available to redistribute the imbalance in moisture, so capillary action must do all the work. Because the paper core contains significant inner moisture, capillarity cannot move the paint down into the paper, so all the movement is sideways across the surface: this produces nicely controlled diffusion effects, and leveling surface flow leads to beautiful, soft backruns. Immediately as the satin texture disappears, spraying tiny drops of water over the paper will create tiny backruns indistinguisable from the texturing effects produced with salt. Added paint or water brings the paper back up to a shiny wetness, but leveling flows do not displace the color already drying on the paper.
In moist paper the surface moisture has evaporated, so there is no surface water: the paper appears dull and unreflective to the eye. However there is still perceptible moisture just underneath the surface, which can be felt as a coolness just above the paper and as wetness to the touch. The paper must again depend on capillary action to redistribute the moisture of added paint, but now capillarity can pull the paint sideways and downwards into the paper, creating smaller backruns and sharper, more raggedy backrun boundaries. Depending on quantity, the added paint brings the paper back up to a satin or shiny wetness, but any significant addition of paint will form a backrun boundary with the surrounding area, which is about to become damp. Even so, a great many delicate and interesting effects are possible at this stage by using diluted paint or water applied with a moist synthetic brush (which transfers very little moisture to the paper); many pigments, especially the sedimentary or granulating iron oxides, cadmiums, cobalts and ultramarines, can be very delicately shaped and shaded using gentle strokes with a damp to thirsty synthetic flat brush. This is also the best time to use drybrush quantities of paint at a raw to syrupy consistency. The sheet can be usefully worked provided that the surface moisture is not increased to a shiny wetness.
The damp paper has lost all its surface wetness and inner moisture near the surface, so there is no perceptible moisture. The paper appears dull and dry to the eye and shows only slight or no coolness to the touch. There is no water to redistribute the paint at the surface, so brush marks can be as sharply defined as they are on dry paper. However, there is still a significant amount of inner moisture deep in the paper, which can be detected as a coolness on the reverse side of the sheet, as a slight softness to the pressure of a fingernail into the sheet, and as a damp limpness in the sheet itself the corner of the paper makes a dull flap if flicked with a finger. Damp paper creates a serious risk: added water or paint (especially creamy to watery paint) migrates by capillary action down into the paper, where it fuses with the damp core. It then replenishes this core (wet into moist), and this expanding reservoir of moisture soaks outwards through the paper fibers and back up to the surface, erupting as random blotching and backruns inside the painted area and as tight, wrinkled backruns or crenelations along its edges. These almost always appear to be unwanted blemishes but can in some situations be expressive. Because these blotches and backruns have emerged from the inner structure of the paper, they cannot be removed by lifting the surface paint! Paper at this stage cannot be worked further and cannot safely be rewetted to a higher level of wetness: you must let the sheet dry completely, and start again.
Finally, the dry paper represents a stable, secure surface for paint application there is no surface moisture and no inner moisture either. All wet in wet effects occur only within the freshly painted area and only by the action of moisture contained in the new paint. Backruns are possible as the paint dries, but only if the surface texture is irregular because of cockling, or the support is very slightly tilted and excess fluid is not wicked up, or the paint was applied very unevenly while the paper is flat. Pigment textures are most visible in this situation, usually with diluted paint and especially with diluted paint applied while the paper is flat, then rocked back and forth a few times before the paint dries to a shiny wetness.
In general, paper at a satin to moist wetness can be worked into some of the most impressive and varied wet in wet effects. However, because moist paper is so delicate, and because water evaporates so quickly from moist paper, the paper puts much greater demands on your observational and painting skills and allows you much less time to act. The opportunities will beckon even though the complex balances will seem insurmountable. But do not give up. With experience you will discover that you learn to control and prolong the paper wetness through the tempo of your painting and the quantities of moisture you add through new paint, and you will learn to adjust your brush and paint wetness to refine images on paper that contains only a hint of moisture. As you strive to master the moist limits of wet in wet painting, the scope and assurance of your skills will noticeably increase.
surface vs. inner wetness
The inner or pulp moisture of the paper is an important dimension of wet in wet painting, but not because it affects the behavior of paint on the paper surface only surface wetness does this.
Instead, inner wetness acts in four ways to alter your habitual frame of reference during painting: (1) it hides from view, which means the painter must rely on indirect clues to determine how much moisture is present; (2) it slows down time by slowing down the transition from one stage to the next during natural evaporation drying, which allows you more time to paint at each paper wetness stage; (3) it adds unpredictable energy or scope of action to paint or water added to the surface, which can produce unpleasant backruns or blotching (in particular, paint applied in the "dry" damp stage will backrun as if the paper were in the "wet" moist stage); (4) it makes forced air drying with a hairdryer or heat gun take longer and produce less consistent results.
The most reliable evidence of the inner paper wetness is your memory of what you've already done with the painting. If you have presoaked the paper, or you have liberally prewetted the paper with sponge or brush, or you have applied a large wash area that has just dried, or you have repeatedly painted over an area with little drying time between coats, or painted any area with a juicy brush, then you have surely increased the inner moisture of the paper. In addition, moist attracts wet: a single wash over completely dry paper increases inner moisture very little, but by the fourth wash more than half the surface wetness goes straight into the already moistened pulp. (Beware: if this tricks you into thinking that the disappearing water has evaporated, you may hastily add new paint to damp paper!)
The next most reliable clue is in the quality of the paper itself. Paper with inner moisture will usually show significant cockling or warping, especially in mouldmade papers and papers made with heavily macerated paper pulp. Cockling occurs because the cellulose fibers absorb water, and as they do the individual cellulose fibers soften and expand lengthwise but not in width, which causes undulations across the grain of the paper. (Handmade papers can also cockle, but usually do so in random, circular humps and depressions.) However, papers will always lose rigidity and become soft and flexible with inner moisture. This softening is readily tested by flicking one corner of the paper with your finger: dry paper will produce a reliable snap, like a playing card; wet paper produces a dull, flappy noise and, with extreme wetness, very little resistance to bending.
The main result of cockling is that paint collects in the surface depressions of the paper and runs off from the raised areas, causing irregularities in the color and in the inner wetness. Because the depressions collect the "run off" water, they stay wetter longer and often spawn backruns that spread from the wet center of the cockle to the moist humps around it.
The traditional cure for cockling is to stretch the paper. Stretching methods were first devised around the turn of the 19th century, when broad wash techniques became more popular and available papers were still comparatively thin (around 190 GSM or less). Today it is possible to control cockling by stretching thinner papers, by buying heavier weights of paper, by allowing the paper to dry completely between large area applications or glazes, and by weighting or bending paper as it dries.
The third clue is less reliable but more important in machinemade or mouldmade papers (e.g., most commercial papers available today). A fresh layer of paint behaves erratically: it shows blotches or backruns when applied to seemingly "dry" paper; it sinks into the paper, dulling as it dries; it diffuses or creeps beyond the brushstroke boundaries; or it bruises when the paint is blotted aggressively with a damp paper towel (photo, right). All these produce unpleasant visual artifacts in the finished work (blotching, dull color, confused edges, dark finger marks). They are almost always signs that you have become inattentive and careless, which means you should take a break from painting while the paper completely dries.
Inner moisture must always be carefully watched in the satin, moist and damp stages of wetness. Applying fresh paint to paper with significant inner moisture content produces backruns or blotching, and these have a distinctive appearance: there is less lightening of the paint caused by pigment migration, there is more irregularity or blotching of the paint color within the backrun, the edges of the backrun are less pronounced, and the backrun shape expands more unpredictably from the brushstroke boundaries. The mark seems almost transparent, in contrast to the grainy, tendrilled backruns in the satin stage that produce complex contour separations between the pigment materials in mixed colors or convenience paints (for example, convenience greens made with yellow iron oxide and phthalo green).
A very important complication: different weights, finishes and manufacturer brands of paper respond differently by absorbing more or less water more or less quickly. Under the same amount of water, some brands of paper will cockle much more than others, or will absorb the surface wetness more quickly. In some papers the surface becomes fragile and very susceptible to sluffing or tearing under scrubbing or scraping, while other papers remain quite tough. Rough (R) papers are usually more absorbent that hot pressed (HP) papers of the same weight, but again this difference is more extreme in some brands and in heavier basis weights. (Lighter weights are usually not less absorbent for their weight they just run out of spongy pulp sooner.) You have to start with papers that give you pretty much the results you want, then learn their wetness quirks through close experience. Once you've established a secure set of skills, you will perceive the differences across papers more quickly and accurately, and can control them more effectively.
balancing wetness in paper, brush & paint
With the most important factor, paper wetness, clearly in view, we can address the other two factors, brush and paint wetness, that combine to create the wet in wet balancing act.
My aim here is to explain the mechanics of wet in wet effects so that you can visualize the connection between the wetness of your materials and the painting result. The section a catalog of marks presents visual examples of all the effects described here, explains how to recognize them, then shows step by step how to create them.
Paper Wetness. Let's start with a simple image of paper wetness, the foundation and catalyst for all wet in wet effects. Imagine wetness as layers of water, with soaked paper represented by many layers of moisture, and damp by only a single thin layer. Dry paper forms the foundation.
paper wetness: the foundation of wet in wet effects
We could also show with this graphic the effect of increased inner moisture (at right): the effective paper wetness is shifted up a level shiny paper behaves like soaked paper, satin paper behaves like shiny paper, and so on down to dry paper, which still has a residual dampness inside. This would remind us that inner wetness shifts the tactile and visual cues of paper wetness, and it prolongs the time it takes for evaporation to shift the paper from one wetness level to the next, adding to the time you can work at each level.
However, to keep things simple, think about an overall paper wetness, which is just the surface wetness alone when the pulp of the paper is dry and is the combined surface and inner wetness when the pulp is wet. If you can accurately judge the wetness of moist or damp paper, then you can predict the effects of paper wetness in wet in wet techniques. But the "caution" sign warns you of trouble if you forget hidden inner wetness and paint on paper that seems "dry enough."
Brush Wetness. By itself, on the paper, the water is quite happy: evenly spread out and evenly evaporating over its entire surface. To create imbalance, we must add a second component to the mix. The best place to start is with brush wetness. This is not exactly the total amount of water or paint in the brush, but is the quantity of moisture that the brush releases onto the paper.
The page on the brush and brushstrokes explains brush wetness in more detail, but here are the main points. Brush wetness is related to three attributes: (1) capacity, or how much water the brush potentially can hold; (2) charge, which is how much water the brush actually contains; and (3) release, which is how quickly and how much of the charge of water in the brush is transferred to the paper during the brushstroke, which produces the total brushstroke length and a characteristic "kiss" or backrun that forms when paint begins to run out somewhere in the middle of the stroke.
Capacity and release are determined by the size and cupping (shape) of the tuft and by the type, length and diameter of hairs or fibers in the tuft. A big brush can hold a larger charge of water and release the water more evenly than a small brush (which quickly coughs up a drop or two and is done); a natural hair brush can hold a larger charge of water and release the water more evenly than a synthetic brush of the same size; the wetness of a synthetic brush can be reduced more precisely and without creating an unwanted "thirstiness" in the tuft, limp squirrel hair can hold more water than thick, stiff pony hair or hog bristle; a flat brush tends to release water less evenly than a round brush of the same capacity; and so on. It is critical to know your brushes intimately.
Notice that I've said water rather than paint throughout this description, because you must judge a brush's capacity and release using pure water, not sticky paint, and because it is the moisture, not the paint per se, that creates a wetness imbalance with the paper. (We explore this point in a later section.)
The Brush/Paper Balance. The effect of brush wetness is easiest to understand if we start with brushes that are only charged with watery paint or pure water. The diagram shows the most important effects of imbalances between these brushes and the paper wetness.
the balance between brush wetness and paper wetness
The key here is to think of the hairs or fibers of the brush tuft in the same way you think about the fibers of cellulose in the paper. When soaked, the paper fibers are completely saturated with water and excess water flows readily on the surface; when soaked, a brush is completely filled with water and excess water flows and drips readily out of the tuft. When damp, the paper surface is completely dry and only the inner fibers remain wetted; when damp, the brush tuft is completely dry but some moisture remains at the center. And so on.
In these terms, when the wetness of the brush is less than the wetness of the paper (top), there is an uptake or wicking of water from the paper surface, along with any dissolved paint. This usually results in a visible blot, color lightening or even a small backrun into the drier area. When the wetness in the brush is greater than the wetness of the paper, there is a significant transfer of liquid from the brush to the paper, and the water must redistribute the imbalance across its surface through flow or backrun.
Because we have available a wide range of brush types and sizes, and we can adjust the amount of water in these brushes from saturated to thirsty, it's pretty obvious that there must be a size and type of brush that can be charged with a certain quantity of water or diluted paint so that the brush wetness and the paper wetness would be the same. In effect, a brushstroke would produce no net flow of liquid from brush to paper or from paper to brush.
This identifies the most fundamental and useful reference point in wet in wet painting: the balance point between paper wetness and brush wetness. If we arrange brush wetness along the bottom of the paper wetness diagram, then this balance point forms a diagonal line from dry brush on dry paper to dripping brush on soaked paper.
the balance point between paper wetness and brush wetness
typical of a #10 to #12 sable round or a 3/4" sable flat on heavy weight, cold pressed (CP) watercolor paper
Obviously, this balance depends on the type of brush and, as already mentioned, the thickness of the paint in the brush; the diagram above is typical for a #10 to #12 sable brush charged with water or watery paint. (The page six degrees of brush wetness explains some of the variations.) However, the key here is to learn how to wet or wick each of your commonly used brushes sable rounds, sable flats, sky wash brushes, squirrel mops, acrylic flats or synthetic rounds, whatever your pleasure so that the brush is at the balance point for any paper wetness. From that point you can "imbalance" the brush by adding or wicking away more water or paint.
To return to the big picture: using a #12 sable round charged with pure water or watery paint, the different combinations of brush and paper wetness produce the effects shown below. The size of the circles shows the vigor and size of resulting backruns; a solid dot indicates no effect.
brush wetness: the engine of backrun effects
This diagram makes three points: (1) backruns occur when brush wetness is greater than paper wetness; (2) as the difference between brush and paper wetness gets larger, the backruns increase in size; and (3) the backrun is most sensitive to the difference between brush and paper wetness when the paper has a satin to moist wetness. Even so, brush wetness (when the brush is charged with water or diluted paint) is the primary control you have over backruns.
A Closer Look at Backruns. Why do backruns occur primarily and most dramatically in the satin to moist range of paper wetness? The key is in the difference between flow and capillary action. When the paper has a soaked to shiny wetness, there is some water available on the surface, and this water can create gravity or leveling flow. As a result, when the brush is applied to paper, flow is sufficient to disperse the paint and equalize wetness, and a backrun cannot form.
At the other extreme, if the paper is too dry, there is not enough moisture in the paper to wick the boundaries of the paint at a rapid pace; the edge of the paint expands very slowly and unevenly, and before the backrun can get rolling the paper has lost water through evaporation; the backrun stops. This produces a characteristic tight, dark, crenelated or crinkled edge.
Paper that is neither too wet nor too dry (at a satin to moist wetness) does not have enough surface moisture for flow to occur, so all movement must happen by wicking along the paper surface and through the many tiny channels inside the paper pulp. But there is enough water already in these channels for the wicking to occur at a rapid rate, and the backrun is steadily pulled forward through these channels. As these channels contain more water than in moist or damp paper, they take longer to dry out through evaporation, which gives the backrun more time to expand and spreads out the water more evenly, producing a softer backrun edge.
"bruises" caused by aggressive blotting of paper with a wet core
There are three different types of backrun (figure at right). The usual or normal backrun occurs when liquid is transferred from the brush to the paper, or when moisture concentrates in one part of the paper due to gradient or leveling flows. This backrun can expand outward from a newer into an older painted area, or it can form inside a freshly painted area or brushstroke. Very small backruns often expand from the "kiss" or greater quantity of water that is released when a brush first touches the support or when it is lifted away while still partly charged; this is especially common on hot pressed (HP) papers. These backruns can also form from the paper edges, especially from water trapped inside folded or wrinkled deckles.
The second kind of backrun, which I call a blot backrun, occurs when moisture is removed from the paper through aggressive wicking or blotting with a damp brush or dry paper towel. The blot backrun is typical when paper at soaked to shiny wetness is blotted down to a satin to moist wetness, as there is enough moisture left inside the paper near the surface, and a large enough difference between blotted and wet area, to provide the wet into moist capillary engine. It is especially common when moderate to high inner moisture is present in the paper: even if all of the surface moisture has been forcefully blotted away, the inner moisture provides the capillary action to pull the surrounding area of wet paint back into the blotted area.
The third kind of backrun, which I call a paint burn, results when "dry" (raw to syrupy) paint is applied to paper at a greater wetness, usually satin to shiny. (Completely saturated or soaked paper usually overwhelms any paint application.) At high concentration, paint can easily contain less moisture than the wet paper surface, so after diffusion has expanded a small halo of color around the paint area, the paper wetness attempts to dissolve and disperse the dense paint. But the water only partly succeeds, leaving undissolved, dense paint at the center, and as the paper wetness goes down, the level of paint concentration sufficient to produce the blemish also goes down. The result is a darkened, dried out, scorched looking patch of dense paint, surrounded by a ragged backrun border, at the center of a diffused halo of paint. The effect is often unsightly or intrusive. Paint burns do not occur on moist to dry paper, because there is not enough moisture to attack the new paint. Instead, the paint bronzes over with a reflective, dark sheen.
All these backruns can also occur through imbalances in the wetness of the paper because the support was tilted, or paint was applied unevenly, or liquid drained into the low points of cockled paper. Techniques for dealing with unwanted backruns are described in the section on controlling backruns.
Paint Wetness (Viscosity). Which brings us to the third piece of the puzzle, the amount of moisture in the paint. This is the same as paint dilution, as described in the page on the secret to glowing color.
Paint viscosity creates two new balance dynamics between paint and paper, and paint and brush. The balance with paper is the more important.
To start, you have to visualize the analogy of paint wetness to paper and brush wetness. paint as a fixed quantity of insoluble pigment particles and carbohydrate molecules (gum, glycerin, sugar) suspended in a fixed quantity of water. Paints straight out of the tube contain a small amount of water as part of their backbone composition, and by diluting the paint you add even more.
I've explained above how you can use the brush/paper balance point as a way to think about brush wetness in the same way as paper wetness, and judge the effects of a wetness imbalance between the two. We can extend this approach to paint as well, as described in the page six levels of paint dilution.
If we take paper wetness as our starting point, the key is to identify the paint dilution that minimizes any diffusion or backrun, when a moderate sized brush is applied to the paper.
the balance point between paint wetness (dilution) and paper wetness
Paint is a quantity of insoluble pigment particles and carbohydrate molecules (gum, glycerin, sugar) suspended in a quantity of water. Dilution is the proportion of water to pigment and vehicle. Paints straight out of the tube contain a small amount of water as part of their backbone composition, and by diluting the paint you add even more.
Most of the water in paints straight out of the tube is tightly clustered around the many organic molecules (gum arabic, glycerin, glucose, honey, dextrin, methyl cellulose, glycols, etc.) that may be in the paint vehicle, which softens these molecules and allows them to dissolve. This water, like the water in a wobbly Jello dessert, does not count as a liquid and cannot contribute to the wetness balance. So raw paint straight out of the tube is close to "dry" in comparison to the paper wetness.
At the other extreme, if we dilute the paint with a large quantity of water, the paint behaves no differently from pure water except for its pale, diluted color. In that case everything we understand about the balance between brush wetness and paper wetness applies the same to paint as to water.
The paint/paper balance point lies at the point where both diffusion and backrun or flow are minimized. The paint takes on the closest possible resemblance to a brushstroke made on dry paper. There may still be substantial redistribution of the paint color, but we have minimized that as much as possible.
The Paint/Paper Balance. Our task, then, in our effort to master wet in wet effects, is to understand paint dilution in terms of its balance with paper wetness. Then a paint/paper imbalance has the effects shown in the diagram.
the balance between paint wetness (dilution)
If the paint is very diluted, then it contains a large amount of free water by volume, and if this wetness is much greater than the wetness of the paper, it creates an imbalance that the paper actively attempts to redistribute, usually as an expanding backrun and/or outward flow. Outward leveling flow especially occurs on moist or damp papers when the quantity of new diluted paint is small, and here the paint will dissolve or lift the damp paint layer(s) below it, producing a distinctive fuzzy, whitened patch. If the surrounding area of paint is "drier" because the paint is more concentrated, there may be inward diffusion will encroach into the new area of more diluted color. In effect, diluted paints can start several different wet mechanisms that can work at the same time and in contradictory ways, leading to very complex effects.
If the paint is very concentrated, then it contains very little water by volume, and if this wetness is much less than the wetness of the paper, it creates a wetness imbalance that the paper attempts to redistribute by diffusion. This can happen in two ways: if the paint is at a moderate dilution (creamy to fluid), contains a significant amount of dispersant, there will be enough liquid in the paint to produce an explosive, large diffusion beyond the brushstroke margins. In contrast, if the paint is very thick (raw to creamy dilution) and there is excess surface water on the paper, the water attempts to flow into the paint area, pushing the diluted paint outward as it does so. Outward leveling flow may also occur on wetter papers, but end result will look very similar to diffusion. In effect, concentrated paints can start fewer redistributing mechanisms, which produce similar visual effects.
We've already looked at the brush/paper balance solely in terms of backruns, so we will distingish paint/paper balance in terms of paint diffusion, as shown below.
paint viscosity: the engine of pigment diffusion and texture
the balance point between brush wetness and paper wetness is not shown because this depends on the paint dilution (see below)
We discover that diffusion is most potent in papers at a soaked to satin wetness, and greatest at a shiny wetness. There is no diffusion on damp or dry paper, and there is diffusion on moist papers only when the brush is heavily charged with liquid. The reason is that diffusion at lower paper wetnesses is driven primarily by flow, which is largely determined by paint quantity, while diffusion on very wet papers is driven by both flow and diffusion of concentrated paint. Both mechanisms act together, and at maximum strength, when the paper contains only small amounts of excess surface water (shiny wetness).
A Closer Look at Diffusion. The indications of maximum paint dilution (for diffusion) along the righthand side of the graphic indicate the approximate paint dilution for the paint/paper balance point at each level of paper wetness.
When the paper is at a soaked to shiny wetness, the amount of excess surface water is so copious that it is very difficult for backruns to form, no matter what the paint quantity. As a result, the only active redistribution mechanism is diffusion or leveling flow (which looks the same as diffusion), and this can occur at almost any paint dilution, so long as the paint is at a significantly higher concentration than the surrounding wet paper. The balance point is relatively high (about 1:40), and all higher concentrations of paint, down to raw paint, will produce diffusion.
At the opposite extreme, paper at a moist to damp wetness contains so little moisture that almost any excess moisture in the paint will induce a backrun or leveling flow. The only remedy is to keep the paint so thick that also contains very little moisture, restoring the moisture balance between paint and paper. As a result, the balance point is at very high paint concentrations (about 1:1 to 1:3). This means diffusion almost never appears at these paper wetness levels, and when it does the spread in color is very small.
The Paint/Brush Balance. The final piece of the puzzle is the relationship between paint wetness and brush wetness or release. In this case a balance does not really exist, because the moisture in the paint is the same thing as the moisture in the brush. Instead, the paint wetness alters the behavior of the brush in several important ways, as shown below.
the balance between paint wetness (dilution) and brush wetness (release)
These effects come down to a simple rule: wetter paint amplifies the brush characteristics. If we compare two identical brushes, one saturated with highly diluted ("wet") paint and the other saturated with highly concentrated ("dry") paint, the brush charged with diluted paint will usually show greater capacity and release onto the paper. The paint amplifies the brush action.
If we then shake out both brushes to make them thirsty, the effect of the paint moisture is complementary: the brush that contained the "wet" paint will show greater wicking action than the brush that contained the concentrated, "dry" paint. Again, the paint amplifies the brush action.
paint wetness (dilution) affects brush capacity and release
This diagram summarizes this amplifying effect for a brush charged to capacity: as the paint becomes more diluted, the capacity and release of the brush increase. There is also an increase in the control of brush wetness through wicking or snapping the brush. If the brush is charged with raw paint, snapping the brush is ineffective, and scraping the paint (wicking) is the only method available to reduce the contents of the brush.
There are a few basic exceptions or limitations to this paint/brush amplifying effect, which have to do with paper wetness.
Paint normally releases from a brush through leveling flow from the thoroughly wet brush tuft to the paper below, then by capillary pull from the hydrophilic cellulose fibers of the wet paper surface into the tip of the brush, and from the tip of the brush up into the core of the tuft, which replenishes paint from the core to the tip as paint is drawn onto the paper during the brushstroke.
Both these mechanisms are reduced as the paint becomes more concentrated, and with thick paints the transfer occurs by mechanical friction of the paper surface actually scraping brush off the tuft. This scraping is increased by pressing the tuft more firmly into the paper during the brushstroke, and by drawing the brush more quickly, so that paint is depleted from the tip before it can be replenished from the tuft core. This also prevents the paint from flowing down into cavities in the paper surface, producing pinholes or scattered white breaks in the brushstroke color, or the streaking, thick color known as drybrush. These effects primarily occur on dry paper, so dry paper provides the widest range of brush release across all paint concentrations.
In contrast, wet paper, especially soaked or shiny paper, inhibits brush control in three ways. It provides a watery envelope in which pinholing or drybrush effects cannot appear, as they are blended or effaced through diffusion as soon as the paint meets the paper. The same envelope somewhat reduces the mechanical action of the paper surface on the tuft, reducing transfer of thick paint. And it easily matches or exceeds the wetness of the brush no matter how much paint the brush contains, eliminating capillary pull of paint out of the tuft and reducing the flow of paint in the brushstroke an effect that increases with diluted paints.
The primary way to counteract these effects is to use a very large brush, such as a sky wash brush, heavily charged with diluted paint, so that leveling flow can pull the paint down onto the paper surface; or to use a smaller brush charged with paint at a creamy dilution, which is thick enough to respond to the mechanical action of the paper surface but thin enough to produce capillary flow of the paint out of the tuft.
These effects are separate from and in addition to the power of excess surface moisture to diffuse the paint beyond any brushstroke boundaries. For this reason, a brush is much less effective as a painting tool on soaked or shiny papers. Instead, soaked papers are most often used to establish very large color areas, created by pouring the paint onto the paper and then shaping, mixing or gradating the paint areas by tilting the paper to create surface flow.
four edge shaping techniques
Wet in wet painting creates irregular, flowing, branching or softly diffusing edges and beautifully shaped color gradations. In fact, wet in wet painting is entirely about dynamic color transitions. But in the typical wet in wet tutorial, painters are told to get the entire sheet of paper really wet, then to plunge in and learn what they can or can't do at each wetness stage as the paper dries.
In my view, this puts the cart before the horse (or the paper before the painter). Wet paper creates an overwhelming skill challenge that painters tackle with unfocused, trial and error learning.
Moreover, as painters working mostly on dry paper, we continuously face the problem of creating a certain kind of edge or color transition, and we don't want to have to soak the entire sheet to get it. These chronic edge challenges lure many watercolor painters into unconscious habits of touching up paint edges as they dry. Usually this grows into a compulsive fussing that only makes the painting look overworked and still doesn't give the desired edge quality.
The remedy is to learn wet in wet techniques in terms of the edge control problems painters encounter in wet in dry painting. By learning how to define and manipulate edges, the painter quickly understands the wetness balance between paper, paint and brush. From that secure beginning, he can go on to produce the desired edge effects in any situation.
Teach Yourself Edge Shaping. Each of the techniques described below includes illustrations of the effects. You must paint along on your own to make sense of how they work.
three types of backruns
backrun (top), blot backrun (middle), and "paint burn" (bottom)
Buy yourself a half dozen or so watercolor medium sized (about 9" x 12") blocks of good quality, cold pressed (CP) watercolor paper from different manufacturers. Prepare the top sheet by drawing a square about 3" x 3" with a graphite pencil or a fine point, indelible marking pen.
Work through the techniques as described, applying paint only within and up to the edges of the square. This will help you keep track of how much diffusion, backrun or color gradation occurs with each method. When you finish a trial on one block, set it aside and start on another block.
By the time you've finished with the sixth block, the first should be dry enough to start another example. After you have filled the sheet, cut it away and start on the next one.
Be sure to use different brushes and different paints (pigments) in different concentrations.
In all cases where water is used, only pure water produces flawless gradations in color. You can use tinted or "dirty" water, but if even trace impurities are present the wetted area will dry as a visibly distinct color area, with edges that need to be managed.
Finally, shaping edges is a delicate visual and physical skill. It is very similar to learning to play a musical instrument. You must observe, explore, and experiment for yourself in order to learn. Practice is the only way to get the essence of the skill that is, the realization that all four edge shaping techniques are simply different expressions of the same wetness imbalances between paper, brush and paint.
Four Edge Shaping Techniques. The illustrations contrast paint (brown) with water (blue), but the same softening techniques work when one type of paint is applied against another though the dynamics of thick into thin will then be an additional complication.
four wet in wet techniques for shaping edges
1: brushing out painted edges with moist brushstrokes; 2: overlapping wetted area into a prepainted area; 3: overlapping painted area into a prewetted area; 4: applying paint entirely within a prewetted area.
There are four ways to control edges with wet in wet techniques:
Overlap Water into Prepainted Area. Viscous to diluted paint is applied to dry paper, then the edges are feathered by painting over them with a wicked brush containing pure water or diluted paint.
Overlap Paint into Prewetted Area. The edge area (but not the area to be painted) is first wetted with pure water or diluted paint, then when the paper has reached the right wetness stage creamy to watery paint is applied to overlap it.
Paint Entirely within Prewetted Area. The entire painting area, including the area to be painted and a substantial area of paper around it, is wetted first, then when the paper has reached the right wetness stage creamy to watery paint is applied into it.
All of these techniques depend on paint diffusion or flow within a wet area to create the color transition. (This is in contrast to the methods of producing graded washes, where the color transitions are produced primarily by changing the dilution or color of paint as you brush it on.) You may sometimes want to allow brushstrokes or backruns as part of an expressive effect, but the only way to master these edge shaping techniques is to master flow and diffusion first, then introduce backrun accents at will.
a practice sheet used to learn
1. Brush Out Painted Edges. This first method is so natural that many artists use it before they are taught to. It produces a relatively uneven, visibly "worked" gradation in the softened edge, which can appear spontaneous, impressionistic or textural if done well, but can appear fussy, overworked and clumsy if done badly. It is probably the most commonly used edge softening method, so we'll look at it in detail.
When to Use. This technique can be used for any size edge, short or long, that can be conveniently softened as you work though you have greater control over the paint along short edges. The goal is to produce a limited edge gradation over a small distance (as if the edge were out of focus or dissolving like the edges of clouds against the sky), and not to create a broad gradation in the color. It works very well with many iron oxide ("earth") pigments or coarsely granulating pigments (cobalt blue, cerulean blue), because these paints diffuse sluggishly and are slow to form backruns. It is less successful with "active" (finely divided) organic pigments or diluted "muddy" or sedimentary pigments (such as cadmium red, venetian red or chromium oxide green) which tend to diffuse excessively and produce backruns readily. (See the page on wash techniques for a discussion of the major pigment types.)
Technique. (1) Apply the paint to dry or premoistened paper, working quickly on a flat surface to produce an even paint application. If necessary to hasten or prolong drying, tilt the paper to drain wet paint away from or toward the edge. (2) Before the edge of the painted area has dried (when it is around a shiny to satin wetness), use a second clean, medium sized, wicked brush to apply pure water along the paint edge. This should be done in gentle, feathering strokes diagonal to the edge, from the painted area into the unpainted (dry) paper. (3) Continue working down the edge. Go back to modify areas already brushed where paint is diffusing too slowly or too quickly, but when possible allow the paint to diffuse untouched into the moistened areas. (4) Tilt the paper or blot with a thirsty brush if necessary to increase or decrease the amount of diffusion into the wetted area, or to drain away excess moisture that might cause backruns into the painted area.
brushing out painted edges
pigments shown are cadmium orange, burnt sienna and phthalo green
Common Problems and Solutions. This edge shaping method almost always produces some brushmark irregularities in the edge gradation or in the color area. So the issue is not eliminating these irregularities, but controlling them for representational purposes, which means increasing or decreasing them at will.
(1) Backruns appear from the wetted area into the painted area. As backruns indicate a wet into moist balancing of paper wetness, the backruns must occur because the wetness of the pure water area was too high in relation to the wetness of the paint: too much pure water was applied, or the paint along the edge had dried too much. The solution is to reduce the wetness of the brush used to shape the edge, or to begin shaping the edge before the paint has dried to the point where backruns appear. Changing to a smaller capacity brush usually increases the visibility of brushmarks. Tilting the support against the backrun is relatively useless, and can start a backrun in the opposite direction.
This problem also commonly arises because the paint has dried more quickly than you expected, causing you to make more aggressive attempts to soften the edge with excess water and repeated brushing. At that point it is best to focus on the edge itself, soften what you can as quickly as you can, then let the color area completely dry. Finish the edge shaping by rewetting the edge and lifting unwanted color with a brush and paper towel.
See also the section on controlling backruns. Once you are able to prevent backruns from forming, you will be able to create them when that is your goal.
(2) Backruns appear from the painted area into the wetted area, or from an inner part of the painted area toward the edge. Backruns from the inner to edge parts of the painted area occur because more paint was applied (or drained into) the inner area than to the edge, or because too much paint was brushed (diffused) away from the edge into the wetted area, causing the edge area to dry more quickly.
(3) Visible brushstrokes remain after the color has dried. This can happen for several reasons: too much pressure was applied to the brush, or the brush was too small or too large, or the brushstrokes were not overlapped to minimize edges, or the brushstrokes strayed too far into the painted area.
(4) There is an unwanted contrast in color or texture between the areas that were brushed and those that were not. Again, the brush was applied with too much pressure or the brushstrokes strayed too far into the painted area. Brushstrokes also become more visible when they are at right angles to the edge rather than parallel to it.
(5) Too much paint diffuses into the wetted area, extending the color farther than intended. The edge was softened while it was too wet or too much paint was applied to the color area. As a result the color diffuses quickly throughout the wetted area. The best remedy is to blot up some of the excess color with a thirsty brush, let the area dry a bit, then add more water along the new edge.
(6) A visible edge forms on the opposite side of the wetted area. This happens either because the water used to shape the edge was already tinted with paint, or because the edge was painted with a finely divided pigment (made of very small pigment particles), such as phthalo blue, iron blue or dioxazine violet. In these paints the very smallest particles can skate along the water surface over considerable distance, and can be moved even farther by capillary flow. This produces a faint but noticeable tinting of the wetted area.
(7) The edge does not diffuse enough, or dries to a hard edge. The edge has dried before it can be wetted with water. Where the paint dries it cannot diffuse.
There are several ways to prevent the paint from drying too quickly. Always paint first the entire interior and "hard" edges of the color area, then paint the edge to be diffused last; or paint the inner area first and then go back to draw the wet paint out to the edges to be diffused. Paint the entire edge quicky so that no part can dry before it is wetted with water; go back with the brush and add slightly more moisture (paint or water) to areas that seem to be drying too quickly. As you paint, tilt the surface toward the edge to be softened, as you would tilt a wash, to delay drying along that edge; then tilt the surface in the opposite direction to draw excess paint away from the edge and back into the area you want to remain solid color, and finally soften the edge with the surface flat.
(8) The edge diffuses unevenly. Some parts of the painted edge are wetter than others, and the wetter areas diffuse more. Use the brush to smooth out these differences in paint wetness before attempting to soften the edge, or use a thirsty brush to blot up excess paint in the areas that have diffused too far.
In this technique the brush wetness is a key factor: a brush with too much water will produce backruns into the painted area, while a brush that is not moist enough will draw the paint out into an area where it quickly dries, making a hard edge that is difficult to adjust further. The correct amount of water depends on the type of pigment, the size of the area of paint, how much the paint has already dried, and how much the edge should be softened (diffused); this is a complex balance that can only be learned by experience. However, the size of area moistened must be at least twice the width of the gradation you want to produce, otherwise diffusing small particles of paint can reach the far edge of the moist area, creating a discoloration where there should only be white paper.
Always rinse and wick the water brush to the same wetness as you work, to ensure a consistent application of clean, clear water across the entire edge to be softened.
The direction of brushstrokes depends on the situation: in general, setting the brush down on the white paper and sweeping the water into the painted area puts more water into the painted area, increasing the likelihood of backruns, while setting the brush down in the painted area and sweeping the water onto the white paper pulls more paint out onto the paper.
Once mastered, the major advantage of this edge softening technique is that edges can be edited or adjusted as you paint, which makes it excellent for landscapes, still lifes and figure studies. In addition, the direction and spacing of brushstrokes can suggest surface contour or texture. For example, softening the edge with many small, parallel, closely spaced strokes can suggest crosshatching or surface roughness of the object shaded; large, aggressively placed strokes can suggest broad, angular changes in surface contour. If one paint is softened with a second, different colored paint, the crosshatching strokes can be used to create varied, almost random color mixtures of the two colors.
brushing out painted edges with moist brushstrokes
2. Overlap Water into Prepainted Area. This is a natural variation on the first method which eliminates the appearance of separate brushstrokes, but at the cost of producing a more irregular, less controllable edge diffusion.
When to Use. This technique is best for small to medium sized edges (6" or less) that can be softened at a precise moment as you work. The paint wetness is critical, which usually means the timing must be accurate and you may have to wait for the edge shaping opportunity. Overlapping water works well with most synthetic organic pigments (which diffuse readily), and also works well with dense pigments (cadmiums), iron oxide (earth) pigments or coarsely granulating (cobalt) pigments, where it can produce a very subtle softening of the edge.
Technique. (1) Apply paint at a creamy to watery dilution to dry paper on a flat surface, working as quickly as possible to produce an even paint application along the edge and from the edge into the center of the painted area. (2) Begin to wet the area around the edge but not touching the edge, starting at least 3" from the edge and working toward it in successive brushstrokes; use a thirsty brush to wick away any excess water once the wetting is completed. (3) When the entire paint edge has dried to a satin wetness, use a wicked , large sized, round or flat brush to apply water along the edge of the paint in a single, even stroke. This stroke should completely join the painted and prewetted areas, and should continually touch the paint edge without straying far into the painted area. (4) Allow the paint to diffuse into the moist area as it dries; tilt the surface if necessary to accelerate or inhibit the diffusion. Blot with a thirsty brush if necessary to manipulate the extent of diffusion.
The image below shows this technique used on four different types of pigment; the join between paint and water was made when the paint was at four different stages of wetness. The satin wetness produces the most consistent results.
overlapping water into painted area
(left to right) cadmium red, benzimida orange, gold ochre and ultramarine violet (all at a fluid paint dilution); (top to bottom) painted area at soaking, shiny, satin or moist wetness when joined with water
Common Problems and Solutions. This edge shaping technique produces a beautiful softened edge with random, atmospheric variations in the extent of paint diffusion and a pronounced tendency for the smallest pigment particles to scatter as a kind of color fog very far into the wetted area. Because the paint is applied to dry paper first, there is almost always a faint trace of the paint edge underneath the diffusing paint, giving the appearance of an edge or horizon viewed through mist, haze or smoke, or an object edge seen through glare or emitting heat or vapor. Backruns, if they form, are usually from the wetted area into the paint, as the paint has had more time to dry, and backruns always tend to form in the opposite direction of active diffusion.
(1) The smallest pigment particles diffuse too far into the wetted area, causing a large discoloration. This can usually be reduced or eliminated by using paints at higher dilution, paints that are made with heavier pigments or larger particle pigments, or paint brands that are formulated without dispersants. Paints made with dense, light, or finely divided pigments and that contain significant amounts of dispersant will produce the largest and most uncontrollable explosion of small pigment particles across the water surface. (The guide to watercolor pigments gives diffusion scores for all paints tested.)
As the examples above show, this pigment scattering increases when the paint is wetter, but for some paints (the cadmium and iron oxide) the scattering is present even when the paint is moist when joined with water.
The discoloration is most noticeable on white, unpainted paper, so it is much less visible if the edge is softened over an area that is already painted or if the wetting is done with a second color of (diluted) paint rather than water. In that case it produces subtle color mixture between the edge and background.
However, the best alternative is to use technique 3 instead. The slight, atmospheric discoloring of the wetted area is typical and should be a desired effect.
(2) Pigment particles diffuse too far into the wetted area, causing a distinct edge at the side opposite from the softened edge. This is another form of the problem just described, and it has the same solutions.
(3) The paint diffusion is too irregular along the edge. This occurs because the paint was too wet or too dense, or had dried unevenly; or the wetted area contained irregular concentrations of water (water was applied unevenly, or drained into cockle depressions in the paper); or the brushstroke joining paint and water varied too much in the release of water (the brush ran out of water or was charged with too much water).
As the examples above show, the irregularity in color diffusion increases significantly and also becomes more unpredictable when the paint is at a greater wetness or is at a higher concentration.
If the brush applied water unevenly, you probably left too large a strip of dry paper between the paint and the prewetted area before the two were joined, so the brush had to wet too much paper. Prewet the paper up to about a quarter inch (1cm or less) from the paint edge. The final stroke should be like a zipper, closing two closely matched areas, rather than a wide bridge between them.
It is important to get an even paint application along the edge so that the entire edge dries to the same wetness when it is joined with the prewetted area. Irregularities most often occur because the edge brushstroke was too long, the brush tuft (capacity) was too small, or the brush had a synthetic tuft; in each case the paint will be applied less evenly along the edge, or the paint will run out before the edge is completed. Always replenish the brush with more paint so that the paint flow from the brush is smooth and even. If two or more strokes are necessary to paint the edge, start the second stroke from the other end and paint toward the middle of the edge; start the third stroke in the middle and paint toward both ends. Connect brushstrokes before the tuft begins to run out of paint and by starting new strokes in an already painted part of the edge. Tilt the paper back and forth to distribute wet paint more evenly along the edge, then tilt the paper so that paint drains away from the edge to decrease drying time. If necessary, prewet the paper before painting the edge, so that the paint and water can be joined immediately after the edge is completed.
When prewetting the paper, use a large squirrel mop or sky wash brush, and drain away excess water by stroking the prewetted area with a thisty brush or tilting the paper and wicking up excess water. Tilting can be used to both distribute water and paint more evenly.
(4) The paint diffuses little or not at all. The edge was wetted when the paint had dried too much. The paint must be at a satin to moist wetness for best results. Make a second, light pass with a wicked brush, this time running the tuft some distance into the painted area but still parallel with the edge, then tilt the paper so that the water will drain away from the edge into the prewetted area. The first pass with the brush will have redissolved some of the paint and this pigment will lift and diffuse with added water. This method can also be used to produce backruns into the painted area along with a softening and diffusion of the paint edge.
(5) The edge still appears too pronounced under the diffused paint. There are four common reasons for this: you are using concentrated rather than diluted paint; you applied too much paint, and therefore had to wait too long for the paint to dry, giving it time to sink into the paper (the issue is not the paint dilution, but the quantity of paint applied to the paper); the paper was too absorbent (it is unpainted paper, there is little or no surface sizing, or the paper surface has been scrubbed); you are using a heavily staining pigment mixture, containing pigments such as phthalocyanine, quinacridone, cadmium or dioxazine.
Use a lighter application of paint or more diluted paint; if a darker color is required, soften the edge on the first light application of paint, then repeat until the color is dark enough. Use a less staining paint, or moisten the paper first to inhibit paint absorption.
(6) Backruns form from the prewetted area into the painted area, or from one part of the prewetted area into another. Excess water was left on the paper, the prewetting was done on moist or damp paper, the imbalance in wetness between paint and water was too large, the paint was too dense or too thinly applied (and therefore dried faster than the water), or the edge was softened when it had dried too much.
Do not attempt to soften the edge over an area of paper still damp from previous soaking or painting, tilt the paper to distribute water evenly and wick up excess water. Try to adjust the wetness of the prewetted area to match the wetness of the paint at the time the two are joined, and try to make the join when both paint and prewetted area are close to the transition from satin to moist wetness.
See also the discussion at controlling backruns.
Combining 1 and 2. In practice, it becomes natural and effective to combine these first two techniques, as required by the painting situation. Most often 2 is effective to start diffusion along the entire edge, then 1 is used selectively to adjust or control the direction or amount of diffusion that occurs, to soften the edge that forms between the single stroke of water and the paint, and to suppress backruns or irregularities by carefully dropping more water or paint into the areas that are still at a satin to shiny wetness.
overlapping water into
3. Overlap Paint into Prewetted Area. This method is easier to control than either of the "brushed out" methods, because the wet to moist diffusion forces are working in the same direction as the thick to thin forces, reducing irregularity along the softened edge. The "fog" of small pigment particles from concentrated paint is minimized.
When to Use. This technique produces the most even edge, especially with moderately diluted (fluid to watery) paints. This makes the edge diffusion more difficult to edit or adjust as the paint dries: the evenness of the diffusion makes any brushmarks more visible. It requires careful preparation of the prewetted area, so it is awkward to use "on the fly" as you paint. Finally, it requires the paper to be perfectly flat to produce an even edge; if possible the edge softening should be done early in the painting, before the paper has cockled with repeated applications of moisture. It is harder to manipulate when mixing two colors (the prewetted area is wetted with a diluted paint), except where the edge is short and connects two bounded color areas for example, the prewetted area is the lighted side of a sphere, and the diffusing edge is the terminator of the dark shadow side.
Technique. (1) With the paper laid flat, generously prewet the paper from about 6" to 8" (15cm to 20cm) outside and up to about 1/4" (1cm) inside the location of the edge you want softened. (2) Paint the edge color shape from the center outwards, up to about 1/4" to the prewetted area. (3) Join the painted and prewetted areas with a single stroke of a lightly wicked brush. If multiple brushstrokes are required to complete the edge, start successive strokes inside the already painted area, paint along the edge until the brush begins to lose paint, then draw the brush back into the already painted area to lift it from the page. Recharge and wick the brush, and repeat as necessary to finish the edge.
overlapping paint into prewetted area
(left to right) cadmium red, benzimida orange, gold ochre and ultramarine violet (all at a fluid paint dilution); (top to bottom) prewetted area at soaking, shiny, satin or moist paper wetness
Common Problems and Solutions. This method produces a more evenly softened edge, at the cost of a more involved preparation (prewetting).
(1) The edge of the prewetted area is visible under the painted area. This happens because the paint was applied to fresh paper. The prewetting removed some of the surface sizing, which affects the paint color. This usually does not happen on papers that have been soaked, stretched and dried before painting. If you do not stretch (for example, you are painting on a watercolor block), first prewet the entire sheet to soften and redistribute the surface sizing, then allow the sheet to completely dry before starting work.
(2) A fog of small pigment particles expands far into the painted area. As explained under technique 2, this can usually be reduced or eliminated by using paints at higher dilution, paints that are made with heavier pigments or larger particle pigments, or paint brands that are formulated without dispersants. (The guide to watercolor pigments gives diffusion scores for all paints tested: choose a paint with a low number.)
(3) A backrun forms into the painted area. This usually occurs because the paint was too dense, so the prewetted area attempts to expand into the painted area to dissolve the paint. The alternatives are to let the backrun form as a decorative effect, or try to break up the backrun as it forms but this will leave visible brushmarks along the edge.
(4) A backrun forms outward from the painted area. This happens because you applied a large amount of relatively diluted paint over a prewetted area that had dried too much. Apply the paint a little earlier, and wick or snap the brush more before painting the edge.
See also the section on controlling backruns.
(5) The edge diffuses more at the point where you start (end) the edge brushstroke. The brush has left a "kiss" or excess release of paint where it first touched or left the paper surface. This can be eliminated by setting the brush down in an already painted area of color, then stroking the brush up to the prewetted area, painting along the prewetted edge, and finally drawing the brush back into the painted area before lifting it off the paper. If you want a point of greater diffusion as an accent along the edge, first paint the entire edge, then draw the brush tip back to that point to lift it off the paper.
overlapping a painted area into a prewetted area
4. Paint Entirely within Prewetted Area. This is the method most painters associate with "wet in wet" painting. It can produce the most diaphanous, poetic and graceful diffusion effects, but it is also the most difficult technique to control.
When to Use. Most commonly used to build large, diffuse areas of color that stand for background mountains, forests or meadows in landscape painting, fogs or mists, and gradations in color that represent changes from light to dark across a scene. It is especially popular in nonrepresentational painting, where it can have a strongly decorative, poetic effect.
Technique. (1) Thoroughly wet the area to be painted, let soak for a few minutes, then drain off excess water by tilting the paper surface and wicking water that accumulates along the lower edge. (2) With the paper laid flat and at a shiny to satin wetness, apply paint to the paper with a brush or by pouring from a small container. (3) Tilt the paper slightly to drive the flow in a specific direction, and allow the paint to diffuse naturally until the paper has dried to a satin wetness. (4) Use a squirrel mop or a spray bottle to increase paper wetness where the paper has dried too soon or diffusion is not spreading fast enough, then tilt the paper back and forth to eliminate brushmarks. (5) Increase the tilt of the paper if you observe irregularities in the paper or paint wetness that will produce backruns, or to dry the paper completely. (6) Tilt the paper surface to drive paint in a specific direction, and wick up excess moisture that collects at the bottom edge. You can also tilt the paper to mix two adjacent areas of wet color, or to accumulate paint where it can be wicked off the paper with a brush.
painting entirely within prewetted area
(left to right) cadmium red, benzimida orange, gold ochre and ultramarine violet (all at a fluid paint dilution); (top to bottom) prewetted area at soaking, shiny, satin or moist paper wetness
Common Problems and Solutions. When the paper surface is soaking, this technique permits the least control over diffusion patterns, and for that reason is preferred in improvisatory styles of painting. When the paper is drier it produces more consistent diffusion across the entire edge boundary, but at the price of significantly greater chance of backruns.
(1) The paint diffuses too far or in an unwanted pattern. The basic problem here is that the paper is flat rather than tilted: gravity flows should be used to shape the direction and extent of the diffusion pattern. Add more paint at the top of the color area to increase color density, wet the center of the color area with a sprayer to increase diffusion, and tilt the paper surface in the opposite direction to retard or reverse diffusion.
Do not demand too much nuance from this method. It produces wonderfully even and subtle mixtures between two color areas, provided that the color areas are not sharply bounded.
If the color must be precisely contained, wet only that area before adding paint, then use tilting and wicking to modulate the amount of diffusion that occurs. When you are satisfied, lay the paper flat to dry to a satin moistness, then tilt slightly (and wick off any excess moisture) to prevent the formation of backruns.
If the paint diffuses beyond the boundary where you want the edge to form, slightly tilt the paper in the opposite direction and begin wicking paint from the diffusing edge. Wick into the color area as necessary to reduce excess paint or water, then tilt the paper back and forth to blur the brushmarks. Return the paper to its original position and let the diffusion continue.
To increase control, apply the paint when the paper is at a satin wetness. As the examples above show, this is the optimal paper wetness to produce an even edge softening without extensive paint diffusion, no matter which type of pigment you use.
(2) "Paint burn" backruns form within the color area. This happens because the paint pigment was too dense either the paint was too concentrated, or the pigment was a dense, powdery type such as the cadmiums, ultramarine, chromium oxide green, carbon black and many red iron oxides (venetian red, indian red). Use a more diluted paint, and compensate for the loss of color by choosing a paint with higher tinting strength or more intense (saturated) color.
(3) Backruns form within the color area. Too much paint was applied for the amount of diffusion the paper wetness could create, and the paper was not tilted slightly so that excess paint could be wicked off.
(4) Backruns form from the wetted area into the color area, or from the color area outward into the wetted area. The imbalance between paper wetness and paint wetness was too great. This often happens when the color has been poured rather than brushed on, or when the wetted area is quite large and some areas have dried before the paint diffusion has stabilized. Working with flat paper rather than tilted paper increases the problem with backruns. Whenever possible, first identify the dominant direction of color gradation (from light to dark, or from one color to another), then tilt the paper so that this direction is parallel with the gravity flow down the page.
applying paint entirely within a prewetted area
Other Tricks or Issues. Pigment attributes play a major role in how you can handle edge shaping. Heavily granulating pigments such as cerulean blue or cobalt violet are relatively slow to diffuse, but also almost never show backruns. This makes shaping the edge with moist brushstrokes (technique 1) the most effective method and the edge relatively easy to control. In contrast, staining, light, or finely particulated pigments such as the phthalos, quinacridones, iron blue and many iron oxides will backrun fairly readily, which makes the method of brushing paint along the edge of drying water most effective.
You must always exercise attentive control over the wet to moist imbalance between paint and water, however they are applied. If the imbalance is too small, or the areas of paint and water are equally wet, then there is a much higher chance of backruns forming because the paint and water will dry at different rates. If it is too large, the paint often will not diffuse as far as you want or will diffuse uncontrollably. The only remedy in these cases is to use your brush aggressively as a moistening and blotting tool, coaxing the paint to move when it is still wet, and blotting up excess moisture or an overexpansive diffusion before it dries.
You will quickly find favorite brushes and tools to use in edge shaping, and you can only do this by trying different brushes based on your success or failure with each technique. I especially like a beefy, 1/2" to 1" sable flat or a medium sized squirrel mop for technique 2, as the stroke is very long and the release of water very even. I prefer a large (#10 to #14) sable round for applying paint in technique 3 and technique 4. I am extremely fond of a #10 or larger squirrel mop for prewetting the sheet and for blending or shaping paint diffusion after paint and water are joined; with a little practice it is possible to get an airbrushed evenness of color gradation with a mop brush.
I can quickly and precisely control the moisture in all these brushes by snapping them with more or less energy I recommend you learn to do the same. Eventually you can acquire a "snap to wetness judgement" that is like the "snap to rebound judgment" which lets you bounce a tennis ball off the floor to any height.
I generally dislike synthetic brushes for edge shaping because the paint/water release is changes too much from the start to finish, and the brushes usually hold less moisture (have a shorter stroke). But I find they are excellent to both apply water and scrub the wet edge if the paint is too staining or has not diffused far enough, and to control small backruns when they appear.
Paper towels are essential general purpose tools for adjusting brush wetness, wicking up excess paper, gently blotting up diffusion that has run too far, and picking up drips and spills. I highly recommend the Kimberly-Clark Kleenex Viva® Towels, marketed under the slogans "strong & soft like cloth" and "the clothlike towel." They really are very strong and highly absorbent; they completely resist shredding or sluffing and will dry out overnight for reuse. Be sure you buy the white, plain (unembossed) sheets; embossed or printed towel patterns can print or transfer to wet paper. Many hardware and automotive supply stores sell a blue shop paper towel of equal durability.
Softened edges are easier to produce on paper that has been premoistened or prepared with two or three previous coats of paint. In this case shaping with a moist brush works much better, because the paint drying time is increased and the layers of paint underneath are not fully bonded to the paper. The drawback is that the colors will muddy more in this situation. Dry, virgin paper stains most easily and can produce uneven results due to random variations in the surface sizing. In that case it is usually better to apply the paint entirely within a prewetted area.
A final trick, which I haven't seen mentioned elsewhere, is to prepare the surface with a foundation glaze of iron oxide pigment. For example, if you lay down an area of flesh tone mixed with a yellow iron oxide (yellow ochre, gold ochre or raw sienna), cobalt blue and a small amount of quinacridone rose, you can easily add areas of warmer color burnt sienna or a quinacridone and shape these with a moist brush. The undercoat of iron oxide particles (the cobalt pigment helps too) redissolves when wetted, and resists backruns, so the quinacridone applied on top can be modified easily.