handprint : carolyn brady

hue purity of watercolor paints

This page publishes my calculations of the hue purity of generic watercolor paint pigments, as explained in the section on hue purity and optimal colors.

This page includes CIECAM coordinates, averaged across all paint brands, for over 170 pigments, including most of those discussed in the guide to watercolor pigments.

The maximum hue purity or MacAdam limit was calculated from the CIE 1964 10° standard observer (Stiles & Burch colormatching functions) under an equal energy (EE) illuminant.

Unclassified mineral pigments, marketed by Daniel Smith as Primatek™ paints, have been included to suggest the range of moderately chromatic natural minerals — that is, the range of inorganic surface colors typical of the environment to which human vision is adapted.

Each row, in order of increasing hue purity, lists:

COLOR INDEX — generic C.I. name of the pigment (this is missing for convenience mixtures and unclassified mineral pigments)
PIGMENT NAME — common pigment name or marketing name
J, a_C, b_C — pigment location in the CIECAM color appearance space
C — CIECAM pigment chroma, defined as (a_C²+b_C²)^0.5
Hue Angle — CIECAM hue angle, defined as ARCTAN(b_C/a_C)
Hue Purity — CIECAM hue purity, the ratio between the pigment chroma and the chroma of the optimal color of matching lightness and hue angle
a_HP, b_HP — ab coordinates for pigment hue purity, scaled so that maximum possible hue purity equals 1.0

All the pigments with the highest hue purity, above 70%, are confined to the orange to red hue span (pyrrole orange PO73, pyrrole scarlet PR255 or pyrrole red PR254), with the sole exception of ultramarine blue (PB29).

The scatterplot below suggests both that optimal colors can be used to further refine the CIECAM chroma estimator, and that optimal colors (physically possible colors) may define an ecologically valid stimulus limit in the adaptation of human vision (and perhaps all terrestrial animal vision).

COLOR INDEX	PIGMENT NAME	J	C	a_C	b_C	Hue Angle	Hue Purity	a_HP	b_HP
.	sodalite	15	3	-3	0	182	0.04	-0.04	0.00
PBr6	iron oxide black	17	7	5	4	38	0.07	0.05	0.04
.	hematite	21	6	-1	6	95	0.08	-0.01	0.08
.	kyanite	41	10	-10	2	170	0.09	-0.09	0.02
.	vivianite	35	12	-9	8	140	0.11	-0.08	0.07
.	jadeite	17	9	-7	6	141	0.11	-0.09	0.07
PBr33	zinc iron chromite brown	25	14	12	8	33	0.12	0.10	0.06
.	bloodstone	22	10	6	8	55	0.12	0.07	0.10
PBk31	perylene green	21	11	-8	8	133	0.13	-0.09	0.09
..	indigo	19	12	-1	-12	267	0.13	-0.01	-0.13
.	purpurite	20	13	13	3	13	0.13	0.13	0.03
.	hematite violet	26	14	10	10	47	0.15	0.10	0.11
.	piemontite	20	16	12	11	40	0.16	0.12	0.11
.	zoisite	22	15	-9	12	128	0.17	-0.10	0.13
.	cote d'azur violet	37	22	14	17	50	0.19	0.12	0.14
.	tiger's eye burnt	23	19	12	15	51	0.20	0.13	0.16
.	green fuchsite	60	29	-25	15	149	0.21	-0.18	0.11
PBr7	burnt umber	28	25	18	16	42	0.21	0.16	0.14
PG17	chromium oxide green	35	24	-18	16	139	0.21	-0.16	0.14
PG8	hooker's green	26	23	-19	14	144	0.22	-0.18	0.13
.	bauxite	24	21	15	16	47	0.22	0.15	0.16
.	apatite	20	16	-14	-8	208	0.23	-0.20	-0.11
PBr7	raw umber	34	23	12	20	59	0.24	0.12	0.21
PR101	mars brown	36	29	20	21	47	0.24	0.17	0.18
PR101	mars violet	25	26	25	10	21	0.24	0.23	0.09
.	red fuchsite	41	31	27	17	32	0.24	0.21	0.13
PR101	lunar red	25	30	26	15	31	0.25	0.21	0.13
.	malachite	50	33	-22	24	133	0.25	-0.17	0.18
.	hematite burnt scarlet	25	32	26	19	36	0.26	0.21	0.15
.	lazurite	26	25	-16	-19	230	0.27	-0.17	-0.21
PG26	cobalt green dark	33	27	-27	0	180	0.28	-0.28	0.00
.	azurite	26	25	-20	-14	215	0.28	-0.23	-0.16
.	serpentine	27	23	-8	22	110	0.28	-0.10	0.27
.	yavapaiite	29	27	14	24	60	0.30	0.15	0.26
PB27+PY35	prussian green	25	27	-25	-8	198	0.31	-0.29	-0.09
PR233	pinkcolor	42	38	34	16	25	0.31	0.28	0.13
PBr41	disazo condensation brown	29	39	33	21	32	0.31	0.26	0.17
PBr25	benzimidazolone brown	31	40	34	21	32	0.32	0.27	0.17
..	hooker's green	33	37	-30	21	144	0.32	-0.26	0.19
.	pipestone	33	43	35	24	35	0.32	0.27	0.19
.	sedona	31	40	30	27	42	0.33	0.24	0.22
PV23	dioxazine purple	20	31	15	-27	299	0.34	0.16	-0.29
..	sap green	33	34	-20	28	126	0.34	-0.20	0.27
PR101	indian red	33	41	37	18	26	0.34	0.31	0.15
PR101	venetian red	31	42	37	19	28	0.34	0.30	0.16
.	tiger's eye	23	15	3	14	77	0.34	0.08	0.34
PR171	benzimidazolone maroon	26	37	36	9	14	0.35	0.34	0.09
PR101	light red	33	44	38	24	32	0.35	0.29	0.18
PBr11	magnesium ferrite brown	40	48	36	32	42	0.35	0.26	0.23
PB60	indanthrone blue	18	32	0	-32	271	0.35	0.00	-0.35
..	olive green	33	31	-5	31	99	0.36	-0.06	0.35
PBr7	burnt sienna	37	48	40	27	35	0.36	0.30	0.21
PG50	cobalt titanate green YS	42	46	-41	20	154	0.36	-0.33	0.16
PY53	nickel titanate yellow	85	46	-2	46	92	0.36	-0.01	0.36
..	naples yellow	75	45	19	41	65	0.37	0.16	0.34
PG19	cobalt green	50	40	-39	-7	190	0.39	-0.38	-0.07
PY119	mars yellow	43	50	34	38	48	0.39	0.26	0.29
PBr7	raw sienna	55	48	23	42	61	0.39	0.19	0.34
PBr24	titanate gold ochre	68	53	24	48	64	0.39	0.17	0.35
PY42	yellow ochre	58	50	22	45	64	0.40	0.17	0.36
PV16	manganese violet	31	44	39	-21	331	0.40	0.35	-0.19
.	green turquoise	30	42	-40	11	164	0.41	-0.40	0.11
PY42	mars yellow	53	50	24	44	61	0.41	0.20	0.36
.	blue turquoise	36	43	-42	-9	193	0.43	-0.42	-0.09
PY42	gold ochre	50	58	37	45	51	0.44	0.28	0.34
PB27	prussian blue	19	40	-17	-36	245	0.45	-0.19	-0.40
PV15	ultramarine violet (red)	36	42	21	-37	299	0.45	0.22	-0.39
PG50	cobalt green [BS]	50	48	-48	0	180	0.45	-0.45	0.00
PY129	green gold	53	49	4	49	86	0.46	0.04	0.46
PG10	nickel azomethine green	58	56	-8	55	98	0.47	-0.07	0.46
PR88	thioindigo violet	29	50	50	-2	358	0.47	0.47	-0.02
PR175	benzimidazolone scarlet	31	56	50	26	27	0.47	0.42	0.21
PO49	quinacridone gold	52	60	33	50	56	0.47	0.26	0.39
PV14	cobalt violet deep	46	47	33	-32	316	0.47	0.34	-0.33
PB27	antwerp blue	35	48	-29	-38	233	0.47	-0.28	-0.38
.	amazonite	30	47	-47	3	176	0.48	-0.47	0.03
PG18	viridian	42	48	-48	3	177	0.48	-0.48	0.03
PO48	quinacridone burnt orange	42	63	52	37	35	0.48	0.40	0.28
..	permanent green light	43	63	-54	32	149	0.49	-0.42	0.25
PG36	phthalo green YS	39	57	-54	18	162	0.49	-0.47	0.15
PB36	cobalt turquoise	39	48	-45	-17	201	0.49	-0.46	-0.17
..	permanent green deep	37	58	-54	22	158	0.49	-0.46	0.19
PY150	nickel azo yellow	67	62	14	61	77	0.49	0.11	0.48
PR206	quinacridone madder	36	60	54	25	25	0.50	0.45	0.21
PV49	cobalt violet light	50	58	52	-26	334	0.50	0.45	-0.22
PG21	[emerald green]	59	61	-57	20	161	0.50	-0.48	0.17
PY117	green gold	58	60	-1	60	91	0.51	-0.01	0.51
PY175	benzimidazolone lemon	83	65	-8	64	97	0.51	-0.06	0.51
PY108	anthrapyrimidine yellow	72	67	14	65	78	0.52	0.11	0.50
PG7	phthalo green BS	31	51	-51	1	178	0.52	-0.52	0.01
PV32	benzamida bordeaux	30	59	56	18	18	0.52	0.50	0.16
PB16	phthalo turquoise	23	44	-36	-27	217	0.52	-0.42	-0.31
PB36	cerulean blue GS	35	52	-39	-34	221	0.53	-0.40	-0.34
PV39	blue violet	20	49	8	-49	279	0.54	0.08	-0.53
PY184	bismuth yellow	87	69	-8	68	97	0.54	-0.06	0.54
PY40	aureolin	77	69	2	69	88	0.54	0.02	0.54
.	rhodonite	36	61	60	13	12	0.55	0.54	0.11
PO65	methin nickel scarlet	33	64	59	25	23	0.55	0.50	0.21
PY1	hansa yellow G	84	70	1	70	89	0.55	0.01	0.55
PY153	nickel dioxine yellow	71	74	29	69	67	0.55	0.21	0.51
PV19	quinacridone violet	27	58	58	7	7	0.55	0.55	0.06
PR179	perylene maroon	29	63	60	21	20	0.55	0.52	0.19
PB15:1	phthalo blue RS	24	54	-23	-49	245	0.56	-0.24	-0.51
PY35	cadmium yellow lemon	89	72	-10	71	98	0.57	-0.08	0.56
PB36	cerulean blue	37	58	-36	-45	231	0.57	-0.36	-0.44
PY55+PY53	diarylide yellow	75	77	23	73	73	0.57	0.17	0.55
PY37:1	cadmium yellow deep	71	77	34	68	63	0.57	0.26	0.51
PY3	hansa yellow light	88	73	-12	72	99	0.58	-0.09	0.57
PY65	hansa yellow deep	77	78	24	75	72	0.58	0.18	0.55
..	phthalo yellow green	55	79	-53	58	133	0.58	-0.40	0.43
PY151	benzimidazolone yellow	84	75	-1	75	91	0.59	-0.01	0.59
PY120	benzimidiazolone yellow	80	75	8	75	84	0.59	0.06	0.58
..	permanent green yellowish	86	75	-11	74	99	0.59	-0.09	0.58
PG50	cobalt teal	56	59	-56	-19	199	0.59	-0.56	-0.19
PB15:3	phthalo blue	27	57	-31	-48	237	0.59	-0.32	-0.50
PY35	cadmium yellow	81	78	11	78	82	0.60	0.08	0.60
PY154	benzimidazolone yellow	83	77	1	77	89	0.60	0.01	0.60
PY110	isoindolinone yellow	72	76	34	68	63	0.60	0.27	0.54
PY35	cadmium yellow light	86	77	-2	77	91	0.60	-0.01	0.60
PY35	cadmium yellow pale	86	77	-4	77	93	0.61	-0.03	0.60
PY139	isoindolinone yellow deep	72	77	35	68	63	0.61	0.28	0.54
PV15	ultramarine violet (blue)	22	57	-4	-57	266	0.61	-0.04	-0.61
PR176	benzimidazolone carmine	32	70	66	24	20	0.61	0.58	0.21
PY138	quinophthalone yellow	82	79	0	79	90	0.62	0.00	0.62
PR149	perylene scarlet	35	74	68	29	23	0.62	0.57	0.24
PR216	brown madder	39	74	68	30	23	0.62	0.57	0.25
PR122	quinacridone magenta	38	71	71	1	1	0.63	0.63	0.01
PY97	hansa yellow	85	80	-2	80	91	0.63	-0.01	0.63
PB15:3	phthalo blue GS	28	60	-36	-48	233	0.63	-0.38	-0.50
PR202	quinacridone magenta	33	70	69	12	10	0.63	0.62	0.11
PO62	benzimidazolone orange	65	77	50	59	50	0.63	0.41	0.48
PR214	scheveningen red deep	33	74	68	29	23	0.63	0.58	0.25
PR264	pyrrole carmine	32	73	69	25	20	0.64	0.60	0.22
PV19	quinacridone rose	44	73	72	13	10	0.64	0.63	0.12
PR83	alizarin crimson	33	73	70	22	17	0.64	0.61	0.19
PB33	manganese blue	46	66	-49	-45	223	0.65	-0.47	-0.44
PV19	quinacridone red	33	75	71	25	19	0.65	0.61	0.21
PR106	vermilion [genuine]	47	80	71	38	28	0.66	0.58	0.31
PO67	pyrazoloquinazolone orange	51	83	68	48	35	0.66	0.54	0.38
PR108	cadmium red deep	36	78	73	28	21	0.66	0.62	0.24
PR178	perylene red	35	79	73	28	21	0.67	0.62	0.24
PO20	cadmium orange	60	82	59	58	44	0.67	0.48	0.47
PB72	cobalt blue deep	29	65	-20	-62	252	0.67	-0.21	-0.64
PV42	quinacridone pink	35	76	74	16	12	0.68	0.66	0.14
PB28	cobalt blue	34	66	-28	-60	245	0.68	-0.29	-0.62
PO69	isoindoline orange	55	84	66	52	38	0.68	0.53	0.42
PR N/A	quinacridone carmine	33	79	74	26	19	0.68	0.64	0.22
PV7+PV15	bright violet	27	73	65	-32	334	0.68	0.61	-0.30
PO71	pyrrole orange	50	85	71	46	33	0.68	0.57	0.37
PB17	phthalo cyan	35	68	-50	-46	223	0.69	-0.50	-0.47
PO34	dizazopyrazolone orange	54	83	71	44	32	0.69	0.59	0.36
PR177	anthraquinone red	33	80	76	24	18	0.69	0.66	0.21
PO5	beta naphthol scarlet	51	87	72	50	35	0.70	0.57	0.40
PO36	benzimidazolone vermilion	48	90	76	49	33	0.71	0.60	0.38
PR108	cadmium red	41	86	78	36	24	0.71	0.65	0.30
PO43	perinone orange	53	88	72	52	36	0.72	0.58	0.42
PR260	vermilion extra	42	87	79	36	24	0.72	0.66	0.30
PO73	pyrrole orange	50	94	75	57	37	0.73	0.58	0.44
PB29	ultramarine blue	21	70	-19	-68	254	0.73	-0.20	-0.70
PR170	naphthol AS red	38	86	81	30	20	0.73	0.69	0.25
PR168	anthraquinone scarlet	44	88	79	39	26	0.73	0.66	0.32
PR251	pyrazoloquinazolone scarlet	43	90	80	41	27	0.73	0.65	0.33
PR209	quinacridone red	46	86	80	32	22	0.74	0.68	0.27
PR9	naphthol scarlet	44	89	81	37	25	0.74	0.67	0.31
PR255	pyrrole scarlet	44	91	81	41	27	0.74	0.67	0.33
PR112	naphthol AS red	43	91	81	42	27	0.75	0.67	0.34
PR108	cadmium scarlet	46	91	80	43	28	0.75	0.66	0.36
PR242	disazo condensation scarlet	44	96	82	49	31	0.76	0.65	0.39
PR188	naphthol scarlet	48	92	81	45	29	0.77	0.67	0.37
PR254	pyrrole red	38	94	85	38	24	0.78	0.71	0.32