What is a single-pigment watercolour?
A single-pigment watercolour is a paint made from exactly one Colour Index (CII) pigment - for example Ultramarine Blue carrying only PB29. The alternative is a multi-pigment “convenience” or “hue” colour, blended from two or more pigments to imitate an expensive, rare or fugitive original. The pigment code on the label tells you which you have: one code is a single pigment; two or more separated by a slash or comma is a blend.
Why single-pigment watercolours mix cleaner
Mixing is a conversation between chemistries. When two single-pigment colours meet on the paper, two chemistries interact - and the result is predictable because you know both of them. When two three-pigment blends meet, six chemistries interact, and the result trends toward grey-brown mud. Single-pigment colours also show their transparency, granulation and staining honestly, because no other pigment is masking the behaviour of the one you chose.
The best single-pigment watercolours, named
These are the single-pigment colours in the Michael Harding watercolour range, drawn live from the published pigment data. Each links to its full product page with lightfastness, transparency and granulation ratings.
| Colour | Pigment | Pigment | Transparency | Lightfastness | Why it’s included |
|---|---|---|---|---|---|
| Titanium White | PW6 | PW6 | Opaque | Excellent | Opaque whites - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PW6; excellent lightfastness. |
| Lemon Yellow | PY175 | PY175 | Semi-Transparent | Excellent | Semi-transparent yellows and oranges - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PY175; excellent lightfastness. |
| Bright Yellow Lake | PY3 | PY3 | Semi-Transparent | Very Good | Semi-transparent yellows and oranges - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PY3; very good lightfastness. |
| Cadmium Yellow Lemon | PY35 | PY35 | Semi-Opaque | Excellent | Semi-opaque yellows and oranges - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PY35; excellent lightfastness. |
| Yellow Benzimidazolone | PY151 | PY151 | Semi-Transparent | Excellent | Semi-transparent yellows and oranges - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PY151; excellent lightfastness. |
| Yellow Lake | PY180 | PY180 | Semi-Transparent | Excellent | Semi-transparent yellows and oranges - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PY180; excellent lightfastness. |
| Hansa Yellow Medium | PY97 | PY97 | Semi-Transparent | Excellent | Semi-transparent yellows and oranges - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PY97; excellent lightfastness. |
| Cadmium Yellow | PY35 | PY35 | Semi-Opaque | Excellent | Semi-opaque yellows and oranges - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PY35; excellent lightfastness. |
| Cadmium Golden Yellow | PY35 | PY35 | Semi-Opaque | Excellent | Semi-opaque yellows and oranges - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PY35; excellent lightfastness. |
| Indian Yellow | PY83 | PY83 | Transparent | Very Good | Transparent yellows and oranges - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PY83; very good lightfastness. |
| Cadmium Yellow Deep | PY35 | PY35 | Semi-Opaque | Excellent | Semi-opaque yellows and oranges - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PY35; excellent lightfastness. |
| Yellow Lake Deep | PY139 | PY139 | Semi-Opaque | Very Good | Semi-opaque yellows and oranges - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PY139; very good lightfastness. |
| Brilliant Orange | PO62 | PO62 | Transparent | Excellent | Transparent yellows and oranges - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PO62; excellent lightfastness. |
| Cadmium Orange | PO20 | PO20 | Semi-Opaque | Excellent | Semi-opaque yellows and oranges - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PO20; excellent lightfastness. |
| Permanent Orange | PO73 | PO73 | Semi-Opaque | Excellent | Semi-opaque yellows and oranges - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PO73; excellent lightfastness. |
| Orange Benzimidazolone | PO36.1 | PO36.1 | Semi-Transparent | Excellent | Semi-transparent yellows and oranges - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PO36.1; excellent lightfastness. |
| Orange Sunset | PO34 | PO34 | Semi-Transparent | Excellent | Semi-transparent yellows and oranges - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PO34; excellent lightfastness. |
| Scarlet Lake Light | PR188 | PR188 | Semi-Opaque | Very Good | Semi-opaque reds and violets - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PR188; very good lightfastness. |
| Cadmium Red Light | PR108 | PR108 | Semi-Opaque | Excellent | Semi-opaque reds and violets - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PR108; excellent lightfastness. |
| Rich Scarlet | PR112 | PR112 | Semi-Transparent | Very Good | Semi-transparent reds and violets - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PR112; very good lightfastness. |
| Scarlet Lake | PR170 | PR170 | Semi-Transparent | Excellent | Semi-transparent reds and violets - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PR170; excellent lightfastness. |
| Cadmium Red | PR108 | PR108 | Semi-Opaque | Excellent | Semi-opaque reds and violets - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PR108; excellent lightfastness. |
| Pyrrole Red | PR254 | PR254 | Semi-Transparent | Excellent | Semi-transparent reds and violets - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PR254; excellent lightfastness. |
| Perylene Crimson | PR149 | PR149 | Semi-Transparent | Very Good | Semi-transparent reds and violets - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PR149; very good lightfastness. |
| Cadmium Red Deep | PR108 | PR108 | Semi-Opaque | Excellent | Semi-opaque reds and violets - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PR108; excellent lightfastness. |
| Pyrrole Crimson | PR264 | PR264 | Semi-Transparent | Excellent | Semi-transparent reds and violets - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PR264; excellent lightfastness. |
| Cinquasia Maroon | PR206 | PR206 | Semi-Transparent | Excellent | Semi-transparent reds and violets - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PR206; excellent lightfastness. |
| Perrindo Maroon | PR179 | PR179 | Transparent | Very Good | Transparent reds and violets - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PR179; very good lightfastness. |
| Rose Madder | NR9 | NR9 | Transparent | Low | Transparent reds and violets - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment NR9; low lightfastness. |
| Alizarin Crimson | PR83 | PR83 | Transparent | Low | Transparent reds and violets - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PR83; low lightfastness. |
| Alizarin Claret | PR177 | PR177 | Transparent | Excellent | Transparent reds and violets - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PR177; excellent lightfastness. |
| Quinacridone Rose | PV19 | PV19 | Transparent | Very Good | Transparent reds and violets - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PV19; very good lightfastness. |
| Quinacridone Coral | PR209 | PR209 | Transparent | Very Good | Transparent reds and violets - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PR209; very good lightfastness. |
| Opera Rose | PR122 | PR122 | Semi-Transparent | Good | Semi-transparent reds and violets - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PR122; good lightfastness. |
| Magenta | PR122 | PR122 | Transparent | Excellent | Transparent reds and violets - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PR122; excellent lightfastness. |
| Cobalt Violet Light | PV14 | PV14 | Semi-Opaque | Very Good | Semi-opaque reds and violets - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PV14; very good lightfastness. |
| Cobalt Violet Dark | PV14 | PV14 | Semi-Transparent | Excellent | Semi-transparent reds and violets - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PV14; excellent lightfastness. |
| Manganese Violet | PV16 | PV16 | Semi-Opaque | Very Good | Semi-opaque reds and violets - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PV16; very good lightfastness. |
| Potters Pink | PR233 | PR233 | Semi-Opaque | Excellent | Semi-opaque reds and violets - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PR233; excellent lightfastness. |
| Quinacridone Purple | PV55 | PV55 | Semi-Transparent | Excellent | Semi-transparent reds and violets - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PV55; excellent lightfastness. |
| Perylene Violet | PV29 | PV29 | Semi-Transparent | Excellent | Semi-transparent reds and violets - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PV29; excellent lightfastness. |
| Ultramarine Violet | PV15 | PV15 | Transparent | Excellent | Transparent reds and violets - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PV15; excellent lightfastness. |
| Deep Purple (Dioxazine) | PV23 | PV23 | Transparent | Excellent | Transparent reds and violets - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PV23; excellent lightfastness. |
| Indanthrone Blue | PB60 | PB60 | Transparent | Excellent | Transparent blues and greens - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PB60; excellent lightfastness. |
| Phthalocyanine Blue Lake | PB15.3 | PB15.3 | Transparent | Excellent | Transparent blues and greens - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PB15.3; excellent lightfastness. |
| Phthalo Blue Red Shade | PB15.1 | PB15.1 | Transparent | Excellent | Transparent blues and greens - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PB15.1; excellent lightfastness. |
| Prussian Blue | PB27 | PB27 | Transparent | Excellent | Transparent blues and greens - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PB27; excellent lightfastness. |
| Cobalt Blue Deep | PB74 | PB74 | Semi-Transparent | Excellent | Semi-transparent blues and greens - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PB74; excellent lightfastness. |
| Cobalt Blue | PB28 | PB28 | Semi-Transparent | Excellent | Semi-transparent blues and greens - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PB28; excellent lightfastness. |
| Ultramarine Blue | PB29 | PB29 | Transparent | Excellent | Transparent blues and greens - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PB29; excellent lightfastness. |
| Lapis Lazuli (Afghan) | PB29 | PB29 | Semi-Transparent | Very Good | Semi-transparent blues and greens - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PB29; very good lightfastness. |
| Cerulean Blue | PB36 | PB36 | Opaque | Excellent | Opaque blues and greens - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PB36; excellent lightfastness. |
| Cobalt Teal Blue Shade | PB50 | PB50 | Semi-Transparent | Excellent | Semi-transparent blues and greens - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PB50; excellent lightfastness. |
| Cobalt Teal | PG50 | PG50 | Semi-Transparent | Excellent | Semi-transparent blues and greens - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PG50; excellent lightfastness. |
| Cobalt Turquoise Deep | PB36 | PB36 | Semi-Opaque | Excellent | Semi-opaque blues and greens - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PB36; excellent lightfastness. |
| Phthalocyanine Green Lake | PG7 | PG7 | Transparent | Excellent | Transparent blues and greens - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PG7; excellent lightfastness. |
| Phthalo Green Yellow Shade | PG36 | PG36 | Transparent | Very Good | Transparent blues and greens - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PG36; very good lightfastness. |
| Terre Verte | PG23 | PG23 | Transparent | Excellent | Transparent blues and greens - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PG23; excellent lightfastness. |
| Terre Verte Blue Shade | PG23 | PG23 | Semi-Transparent | Excellent | Semi-transparent blues and greens - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PG23; excellent lightfastness. |
| Cobalt Green Deep | PG19 | PG19 | Semi-Opaque | Very Good | Semi-opaque blues and greens - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PG19; very good lightfastness. |
| Viridian | PG18 | PG18 | Transparent | Excellent | Transparent blues and greens - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PG18; excellent lightfastness. |
| Oxide of Chromium | PG17 | PG17 | Opaque | Excellent | Opaque blues and greens - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PG17; excellent lightfastness. |
| Perylene Green | PBk31 | PBk31 | Semi-Transparent | Very Good | Semi-transparent blues and greens - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PBk31; very good lightfastness. |
| Green Gold | PY129 | PY129 | Transparent | Excellent | Transparent blues and greens - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PY129; excellent lightfastness. |
| Turners Yellow | PY216 | PY216 | Semi-Opaque | Excellent | Semi-opaque browns - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PY216; excellent lightfastness. |
| Ochre Icles Lemon | PY43 | PY43 | Semi-Opaque | Excellent | Semi-opaque browns - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PY43; excellent lightfastness. |
| New Gamboge | PY150 | PY150 | Semi-Transparent | Excellent | Semi-transparent browns - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PY150; excellent lightfastness. |
| French Yellow Ochre | PY43 | PY43 | Semi-Transparent | Good | Semi-transparent browns - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PY43; good lightfastness. |
| Raw Sienna Light | PBr7 | PBr7 | Semi-Transparent | Good | Semi-transparent browns - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PBr7; good lightfastness. |
| Raw Sienna Dark | PBr7 | PBr7 | Semi-Transparent | Good | Semi-transparent browns - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PBr7; good lightfastness. |
| Transparent Oxide Yellow | PY42 | PY42 | Transparent | Good | Transparent browns - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PY42; good lightfastness. |
| Yellow Ochre | PY42 | PY42 | Semi-Transparent | Excellent | Semi-transparent browns - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PY42; excellent lightfastness. |
| Naples Yellow | PBr24 | PBr24 | Semi-Opaque | Excellent | Semi-opaque browns - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PBr24; excellent lightfastness. |
| Yellow Ochre Deep | PY43 | PY43 | Semi-Transparent | Excellent | Semi-transparent browns - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PY43; excellent lightfastness. |
| Italian Brown Ochre | PBr7 | PBr7 | Semi-Transparent | Very Good | Semi-transparent browns - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PBr7; very good lightfastness. |
| Italian Burnt Ochre | PBr7 | PBr7 | Semi-Transparent | Good | Semi-transparent browns - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PBr7; good lightfastness. |
| Burnt Sienna | PR101 | PR101 | Transparent | Excellent | Transparent browns - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PR101; excellent lightfastness. |
| Pozzuoli Red | PR101 | PR101 | Semi-Transparent | Very Good | Semi-transparent browns - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PR101; very good lightfastness. |
| Herculane Red | PR101 | PR101 | Opaque | Excellent | Opaque browns - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PR101; excellent lightfastness. |
| Red Ochre of France | PR102 | PR102 | Opaque | Excellent | Opaque browns - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PR102; excellent lightfastness. |
| Puisaye Hematite | PR102 | PR102 | Opaque | Very Good | Opaque browns - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PR102; very good lightfastness. |
| Earth of Cyprus | PBr7 | PBr7 | Semi-Transparent | Good | Semi-transparent browns - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PBr7; good lightfastness. |
| Transparent Oxide Brown | PBr7 | PBr7 | Semi-Transparent | Excellent | Semi-transparent browns - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PBr7; excellent lightfastness. |
| Permanent Brown | PBr25 | PBr25 | Transparent | Excellent | Transparent browns - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PBr25; excellent lightfastness. |
| Red Umber | PBr6 | PBr6 | Semi-Transparent | Very Good | Semi-transparent browns - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PBr6; very good lightfastness. |
| Burnt Umber | PBr6 | PBr6 | Semi-Transparent | Excellent | Semi-transparent browns - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PBr6; excellent lightfastness. |
| Indian Red | PR101 | PR101 | Semi-Opaque | Excellent | Semi-opaque browns - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PR101; excellent lightfastness. |
| Dark Morellone Earth | PR101 | PR101 | Opaque | Excellent | Opaque browns - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PR101; excellent lightfastness. |
| Raw Umber | PBr6 | PBr6 | Semi-Transparent | Very Good | Semi-transparent browns - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PBr6; very good lightfastness. |
| Van Dyke Brown | PBr8 | PBr8 | Opaque | Very Good | Opaque browns - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PBr8; very good lightfastness. |
| Titanium Buff | PW6.1 | PW6.1 | Semi-Opaque | Excellent | Semi-opaque browns - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PW6.1; excellent lightfastness. |
| Vine Black | PBk11 | PBk11 | Semi-Transparent | Excellent | Semi-transparent greys and blacks - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PBk11; excellent lightfastness. |
| Lamp Black | PBk6 | PBk6 | Opaque | Excellent | Opaque greys and blacks - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PBk6; excellent lightfastness. |
| Ivory Black | PBk9 | PBk9 | Semi-Transparent | Excellent | Semi-transparent greys and blacks - a true single-pigment watercolour that mixes cleanly because only one chemistry is at work. single pigment PBk9; excellent lightfastness. |
How to read a pigment code
The Colour Index code identifies the exact pigment regardless of who made the paint. The letters denote the colour family: PB blue, PR red, PV violet, PY yellow, PG green, PBr brown, PW white, PBk black, PO orange. A single code means one pigment; multiple codes mean a blend. If the label carries no code at all, the contents are undisclosed and you cannot verify how the colour will mix or age.
When a multi-pigment hue is acceptable
A multi-pigment “hue” is a legitimate substitute when the genuine single pigment is fugitive (the original Gamboge), prohibitively expensive (genuine Vermilion), or no longer manufactured. Used straight for a specific effect, a good hue is perfectly serviceable. The problem comes when convenience colours are mixed further - three or four chemistries interacting on the paper is where mud begins. For a working palette built to mix, favour single pigments and reach for a hue only when no stable single pigment will do.
Frequently asked questions
What are the best single-pigment watercolours?
The best single-pigment watercolours are those made from one Colour Index pigment and taken to a high pigment load: Ultramarine Blue (PB29), Phthalocyanine Blue (PB15), Quinacridone Rose (PV19), New Gamboge (PY150), Burnt Sienna (PBr7), Viridian (PG18) and Cadmium Red (PR108). Single-pigment colours mix cleanly because only one chemistry interacts with others on the paper, and they show their transparency, granulation and staining honestly.
What is a single-pigment watercolour?
A single-pigment watercolour is a paint made from exactly one Colour Index (CII) pigment - for example Ultramarine Blue carrying only PB29. The alternative is a multi-pigment "convenience" or "hue" colour, blended from two or more pigments to imitate an expensive or fugitive original. Single-pigment colours mix predictably and reveal each pigment's true behaviour.
Are single-pigment watercolours better?
For clean, predictable mixing and for seeing each pigment's true transparency, granulation and staining, yes - single-pigment watercolours are better. They let you build a palette from known chemistries rather than mystery blends. Multi-pigment convenience colours are acceptable when a genuine single pigment is fugitive, prohibitively expensive, or unavailable - but they muddy quickly if mixed further.
Does Michael Harding make single-pigment watercolours?
Yes. Michael Harding watercolours lean toward single-pigment formulation so each tube behaves predictably and mixes cleanly. The Colour Index pigment code is published on every product page, so painters can see at a glance whether a colour is single-pigment (one code) or a blend (several).
How can I tell if a watercolour is single-pigment?
Read the Colour Index (CII) code on the label. A single code (e.g. "PB29") means one pigment; two or more codes separated by a slash or comma (e.g. "PV19 / PR122") mean a blend. If the label carries no pigment code at all, the manufacturer has not disclosed the contents and you cannot verify how the colour will mix or age.
When is a multi-pigment watercolour acceptable?
A multi-pigment "hue" is acceptable when it substitutes for a pigment that is fugitive (the original Gamboge), prohibitively expensive (genuine Vermilion), or no longer manufactured. Used straight for a specific effect they are fine; the problem comes when they are mixed further, because three or four chemistries interacting on the paper is where mud begins.
