Lightfastness in watercolour: which pigments last

title: “Lightfastness in watercolour: which pigments fade and which hold”

slug: lightfastness-in-watercolour

focus_keyword: lightfastness in watercolour

title_tag: “Lightfastness in watercolour: which pigments last”

meta_description: “Lightfastness in watercolour determines which paints survive the years and which fade within months. A plain-English guide to ratings, pigment codes, and what to buy.”

secondary_keywords: watercolour lightfastness, ASTM watercolour rating, permanent watercolour pigments, fugitive watercolour paint

Lightfastness in watercolour is not a technical nicety. It is the difference between a painting that holds its colour for a generation and one that looks washed out within a few years of being hung near a window. The question of which paints will last is simpler to answer than most advice suggests, once you know where to look and what the numbers mean.

At a glance

Lightfastness measures resistance to fading under light exposure. ASTM I is excellent. ASTM V is very poor. Most artist grade ranges contain mainly ASTM I and II rated colours. Those two categories are the ones to build a palette from.

The rating systems are not the same across brands. Winsor and Newton’s AA rating and Daniel Smith’s ASTM I are broadly comparable but not identical. Check the specific rating on the manufacturer’s page rather than assuming equivalence across systems.

Some traditional colours are fugitive. Certain reds, violets, and oranges in student grade ranges use pigments with poor lightfastness. The colour name alone does not tell you this. The pigment code does.

Most earth pigments are permanent. Iron oxide pigments, including the yellow ochres (PY43), raw and burnt umbers (PBr7), and the siennas, are among the most lightfast colours available. A palette built around them carries very little fading risk.

Framing under UV-filtering glass significantly extends the life of any watercolour. Lightfastness testing is conducted under direct, concentrated exposure. In normal display conditions with UV protection, even moderately lightfast colours last considerably longer than test results alone suggest.

What lightfastness ratings actually measure

Lightfastness is a measure of how much a colour changes when exposed to light over time. The tests are standardised, which means the results are comparable, at least within a single rating system.

The most widely used standard for artists’ materials is the ASTM system, developed by ASTM International. Paints are exposed to a controlled light source and assessed for how much the colour shifts. The results fall into five categories: ASTM I is excellent, ASTM II is very good, and anything rated III or below represents increasing degrees of fading risk. For finished, permanent work, ASTM I and II are the categories that matter.

What the rating does not measure is everything else that affects a painting’s longevity: the quality of the paper, the acidity of the support, humidity, temperature, or how the work is stored and displayed. A rating applies to a manufacturer’s finished paint, not to a pigment in the abstract: pigment concentration, binder and formulation are part of the tested result. Pigment identity remains an important clue, especially for consistently stable families such as ultramarine, iron oxides and phthalocyanines.

Rating systems and how they compare

Two systems appear most often on watercolour packaging sold in the UK.

The ASTM system rates finished paints on the I to V scale described above. Daniel Smith publishes ASTM ratings for each colour in their Extra Fine range.

Winsor and Newton use their own permanence scale: AA, A, B, and C. AA and A are the ratings to trust. B indicates moderate durability. C indicates the colour is fugitive and unsuitable for permanent work. Winsor and Newton’s permanence rating is not a direct translation of ASTM scores. It incorporates additional factors, including binder stability and pigment manufacturer data, which means their AA designation reflects more than the ASTM test alone captures. Winsor and Newton also note that an A-rated colour applied in a very thin wash may behave differently from the same colour at full strength, which is worth keeping in mind for painters who work with heavily diluted mixes.

The practical conclusion is that the two systems are not directly interchangeable. Do not compare a Winsor and Newton A rating with a Daniel Smith ASTM II and assume they are the same thing. Each system has its own criteria. Use the rating to evaluate colours within a brand, not to rank one brand against another.

Some European brands use the Blue Wool Scale, a separate test method based on eight dyed wool references with increasing resistance to fading. Schmincke, for example, converts Blue Wool results to its own star scale. There is no official conversion between Blue Wool values and ASTM categories, so treat a brand’s published system as its own evidence rather than trying to translate one rating directly into another.

Which pigment families are most likely to fade

Certain pigment families carry a higher fading risk than others, and watercolour is particularly exposed because the pigment particles sit on the paper surface rather than being suspended in a thick binder layer.

The red and violet range presents the most risk. Alizarin Crimson (PR83) is one of the most well-documented fugitive pigments in traditional watercolour. Its current rating should always be checked against the manufacturer’s published chart, but it is not generally chosen for a permanent palette. Rose Madder Genuine is another historical red that should be checked against current manufacturer information before use.

Opera Rose and Opera Pink are used frequently in contemporary watercolour work because of their vivid, high-key character. Their current rating should be checked against the manufacturer’s chart; they are not generally colours for work intended to last.

Some violets and bright oranges in student-grade ranges also use fugitive organic pigments. The colour name on the tube does not tell you which pigment is inside. That information is on the label, usually as a two or three letter prefix followed by a number.

The simplest check before buying a new colour: find the ASTM or permanence rating on the manufacturer’s website before it goes on your palette. Most publishers show this clearly. For Winsor and Newton, AA and A. For Daniel Smith, ASTM I and II. Below those thresholds, the colour is for studies, not finished work.

Which pigments are reliably permanent

The earth pigments are where stability starts. Yellow Ochre (PY43), Raw Sienna (PBr7 or natural iron oxide equivalents), Burnt Sienna (PBr7), Raw Umber (PBr7), and Burnt Umber (PBr7) are iron oxide pigments with a long track record of permanence. They pre-date synthetic pigments by centuries and remain among the most reliable colours available. These are not merely safe choices on lightfastness grounds. They are also among the most behaviourally interesting pigments in watercolour, with the granulation and texture that many painters work deliberately with.

Among the blues, Ultramarine (PB29) and Cerulean (PB35 or PB36) are reliably permanent. Prussian Blue (PB27) has excellent lightfastness, though it can undergo reversible photoreduction, appearing to fade in low light or darkness and recovering on re-exposure. French Ultramarine, regardless of brand, is among the most stable pigments in the range.

The phthalo family, including Phthalo Blue (PB15) and Phthalo Green (PG7), are synthetic pigments with excellent lightfastness ratings across all major manufacturers. They are also intense and staining, which has practical implications for mixing, but as far as permanence goes they are unproblematic.

Among the modern synthetic organics, the quinacridone pigments (PR206, PV19, PO49 and relatives) offer excellent lightfastness combined with good transparency, which is why they have largely displaced traditional alizarin-based reds and violets in permanent palettes.

For a deeper look at pigment codes and what the prefixes tell you about a colour’s chemistry, the article on pigment codes explained is the place to start.

How to check a colour before you buy it

Most major manufacturers publish permanence information on their websites and on the tube itself.

For Winsor and Newton Professional Watercolour, the permanence rating appears on the label as AA, A, B, or C. Their website lists ratings for every colour in the range.

For Daniel Smith Extra Fine Watercolour, ASTM ratings are published in their pigment characteristics document alongside pigment codes, transparency, granulation and other properties.

For any unfamiliar colour in any range, the sequence is: find the pigment code on the label, check the manufacturer’s published ASTM or permanence rating for that specific product, and if the information is absent or unclear, treat the colour as a study paint rather than a palette staple until you can verify it.

The materials section of this site covers individual pigment families and how they behave in more detail.

The practical verdict

The paints most likely to fade are the ones with a long tradition of being beautiful and problematic: Alizarin Crimson, Rose Madder, Opera Rose. They appear in painters’ arsenals because the colours are genuinely difficult to replicate with permanent alternatives at the same intensity. For study work or paintings that will not be displayed long-term, that may be an acceptable trade. For anything intended to last, the permanent alternatives exist and perform well.

The safest part of the palette, and the part with the most interesting surface behaviour, is also the oldest: the iron oxide earth colours have been permanent for longer than any rating system has existed to confirm it.

Framing finished work behind UV-filtering glass extends the life of any pigment, permanent or otherwise. Lightfastness testing is conducted under more aggressive exposure conditions than a painting on a domestic wall typically experiences. The ratings are a guide to relative risk, not a prediction of exactly how many years a particular colour will survive in your specific room. Manage the display environment as well as the pigment choice, and the two together do most of the work.

Lightfastness in watercolour: which pigments fade and which hold