12 : yellow ochre (PY43), raw umber (PBk7), nickel azomethine yellow (PY150), burnt sienna (PBr7), burnt umber (PBr7), gold ochre (PY42), cadmium vermilion (PR108), light red (PR101), quinacridone carmine (PR N/A), indanthrone blue (PB60), iron blue (PB27), ivory black (PBk7) or india ink Watercolor paintings from the 18th century and earlier display a color gamut that is limited by the pigments available at the time. A number of artists and drawing handbooks of the era describe a typical selection of paints: I've chosen modern substitutes for the most common choices as a "classical" watercolor palette.
The classical palette "footprint" is essentially the Velázquez palette expanded by "warm" pigments with more chroma and a wider range of hues. The 18th century choice of natural earth pigments typically included raw sienna and Vandyke brown or Cologne earth. I've replaced raw sienna with raw umber (PBr7) to get a greater contrast with yellow ochre PY43), and replaced the dark brown with burnt umber (PBr7), as most vandyke brown watercolors are just convenience mixtures of burnt umber and lamp black.
Classical palettes often contained alternative earth reds, which I've limited to the single (nearly universal) choice of the most saturated red earth, light red (PR101); Daniel Smith's terre ercolano is also an effective choice. (If the paint brand you prefer does not offer a light red, use venetian red instead.) It may also be convenient simply to choose the traditional earth quartet (raw sienna, burnt sienna, raw umber and burnt umber), plus a red earth such as venetian red, from a single paint manufacturer. Each brand selects and balances these colors to provide a distinctive range and contrast within the group.
Natural lapis lazuli pigment was much too expensive for common use, cobalt blue was not available until the early 1800's and artificial ultramarine only after 1830, so 18th century painters made do with an extremely limited choice of cool pigments. Most artists relied heavily on the natural organic blue pigment indigo and some adopted the greener and far more lightfast iron (prussian) blue (PB27) after it became available in the 1730's. Unfortunately, the hue of modern imitation indigos is less flexible than genuine indigo classical painters apparently could mix an olive green from indigo and burnt sienna (!). I've substituted indanthrone blue (PB60), which can recreate indigo's near violet darks, though it forces all the green mixing tasks onto iron blue. Blue is also essential to mix near neutral (gray) colors: iron blue and indanthrone blue work equally well with burnt sienna, light red and burnt umber.
Despite recent prejudice against them, both a white and black pigment were used to adjust values values. White pigment was used to strengthen color highlights and build opaque figures on top of already painted areas, and for that task titanium white (PW6) is a great improvement over lead carbonate (PW1), the classical white, which turns brown if exposed to sulfur pollution. Most watercolorists used more than one transparent, staining black or bistre paint (or india ink) to wash in the basic value structure of the picture; I've only included a common carbon black paint.
The pigment selection so far was fairly common among 18th century artists. There was more disagreement among artists in the selection of brighter colors on the warm side of the color wheel; I've illustrated four typical choices. (1) Many artists used genuine gamboge, which is closely matched in color and transparency by the modern pigment nickel azomethine yellow (PY150). Gamboge, raw sienna and yellow ochre mixed with indigo or iron blue provided all the greens a painter needed; green pigments were almost never used before the 19th century. (2) A few sources mention the poisonous deep yellow pigment orpiment in its orange shade, available since the early 18th century, which I've replaced by gold ochre (PY42) which has a very similar hue, chroma and opacity. (3) A cadmium scarlet (PR108) is the closest modern replacement for poisonous and fugitive vermilion (PR106), which was (like orpiment) a less popular palette choice and always used very sparingly, in mixtures or tints, or as small color accents. (4) Finally, most artists also chose a carmine lake to mix more saturated red and violet hues and to warm the blues; I've substituted quinacridone pyrrolidone (PR N/A). All these paints must harmonize with the earth hues, and (before the Romantic period) were rarely visible in a painting as undiluted or pure colors.
If the classical palette is so limited, why bother with it? It is first of all useful background to understand the historical traditions of your art. The demonstration painting is by Francis Towne, a master of subtle color and elegant design. The page on Towne's art describes the classical methods of watercolor painting, which make effective use of the classical color range. (See also the discussion of the topographical tradition and the limited color schemes of John Robert Cozens.) All these 18th century painters used slightly different (and sometimes even more limited) palettes than the one I've suggested, but their works illustrate the gentle, elegaic mood characteristic of the classical palette.
A second benefit is that it teaches you the power of muted hues. Like the Velázquez palette, the classical palette's limitations are its strengths when it comes to representing atmosphere and illumination. This is well illustrated in Towne's painting. The classical palette also exemplifies the fundamental and effective watercolor strategy of representing dark values with transparent, muted, cool colors (to give them air and light) and representing light values with opaque, warm colors (to give them substance and form).
Third, the classical palette is capable of a very affecting and subtle poetry if you can create an effective variation of values and color temperature to compensate for the limited range of hue and saturation. Skillful use of near neutral colors is preached by workshop painters such as Jeanne Dobie or Stephen Quiller the classical palette really puts that skill to work.
The final benefit is simply expanding your artistic imagination. Like it or not, we have been culturally conditioned ever since the early 19th century to prefer bright colors, and this prejudice blinds us to what is possible in a muted key. Many 18th century painters believed that "bright colors are ill advised and should always be avoided," as a tutorial of the time put it. Painters of the time did not see the classical palette as a poverty of pigment choices but as a virtuous color restraint. This understatement and subtlety can have powerful emotional resonances in our culture of strident color extremes.