Paint Pigments and Lightfastness: A Practical Guide for Artists

What lightfastness actually means

Lightfastness is a pigment's resistance to fading or shifting when exposed to ultraviolet and visible light. It is not a property of the brand or the binder; it is a property of the pigment itself. The same Permanent Rose pigment behaves the same way whether it is in oil, acrylic, or watercolour.

Two rating systems matter in art materials:

• ASTM D4303. The American standard. Rates pigments from I (excellent) to V (very poor). I and II are considered permanent for fine art use; III is borderline; IV and V are fugitive and should be avoided in anything you sell.
• Blue Wool Scale. The European standard. Rates from 1 (very poor) to 8 (excellent). Most fine art manufacturers consider 6 and above acceptable, with 7 and 8 being archival quality.

Many manufacturers also use their own internal scale (such as a star system from one to four). These are usually a translation of ASTM or Blue Wool, but they are not always equivalent across brands. When in doubt, look for the underlying ASTM rating on the tube or the manufacturer's technical sheet.

How to read a tube label

Every artist-grade paint tube includes the information you need, if you know where to look. The four things to find:

1. Pigment code. A letter and number combination such as PB29 (ultramarine blue) or PR108 (cadmium red). This identifies the actual chemistry.
2. Lightfastness rating. Usually printed near the pigment code, sometimes as a number, sometimes as a star rating.
3. Series number. Indicates the price tier, which often correlates with pigment quality and concentration.
4. Single pigment or mixture. A tube with a single pigment code is generally cleaner to mix with than a tube with three or four codes.

Pigments to avoid in finished work

A handful of pigments are still widely sold despite poor lightfastness. They have a place in studies and sketchbook work, but they should not appear in paintings you sell or exhibit. The most common offenders:

• Alizarin Crimson (PR83). Beloved for its deep transparent red, but classified ASTM III at best. The genuine version fades. Most modern alternatives use a quinacridone (PR202 or PV19) and are sold as Permanent Alizarin or similar.
• Opera Pink (PR122 with fluorescent dye). Beautiful in watercolour. Gone within a few years on a sunlit wall.
• Aureolin (PY40). Loved by traditional watercolourists. Known to darken and shift over time.
• Hansa Yellow Light (PY3). Some versions are fine, others fade. Check the specific brand's lightfastness data.
• Some daylight fluorescent colours. By design they cannot meet archival standards. Use them deliberately or not at all.

The presence of a fugitive pigment does not mean a painting is worthless, but it does mean you owe the buyer disclosure if the painting was made for permanence.

Other archival considerations

Lightfastness is the headline issue, but a few other pigment properties affect how a painting ages:

• Tinting strength. How much a pigment dominates a mixture. Phthalos are extreme; earth colours are mild. Tinting strength affects how predictable your mixes are.
• Drying rate. Some pigments speed drying (umbers, cobalt) and some slow it (cadmiums, titanium white). Mixing fast over slow can cause cracking later.
• Opacity. Important for layering decisions, especially in oil painting where fat over lean rules apply.
• Health and toxicity. Cadmiums, cobalts, and lead-based pigments are perfectly safe in normal studio use, but they require sensible handling. Avoid sanding dried paint, do not eat near the palette, and dispose of rags and solvents responsibly.

Document the materials in each painting

A painting that lives for fifty years will be examined by conservators, insurers, and buyers who never met you. The most useful thing you can leave them is a clear record of what is actually in the work. At minimum, note:

• The pigments used, by name or pigment code.
• The medium (oil, acrylic, gouache, mixed).
• The ground and support (linen, cotton, panel, paper).
• Any varnish applied, including the type and date.

A line on the back of the painting is a start. A dedicated inventory entry is better, because it survives reframing, lining, and the slow disappearance of pencil from canvas backs. This is part of why consistent inventory records matter beyond the moment of sale.

A simple pigment audit

Once a year, pull every tube out of your studio and write down the pigment code and ASTM rating from each label. Most artists are surprised by how many tubes have a III or IV rating they had never noticed. Replace the worst offenders with permanent alternatives.

You do not need to eliminate every fugitive pigment. You need to know what you are using, where it sits in your work, and what to tell buyers. That is the difference between an archival practice and a hopeful one.