How to use the Pigment Lightfastness Lookup
- Find the code on your tube. Pigments are identified by a Colour Index code printed in small type on the label:
PB29is Pigment Blue 29,PR101is Pigment Red 101,PBr7is Pigment Brown 7. - Look it up in Browse pigments. Type the code or a name into the search box, or narrow the table with the color chips and the Lightfastness filter. Each row shows the typical ASTM rating, opacity, how much it stains in watercolor, and a note on handling or quirks.
- Check a whole palette at once. Open Check my palette, paste one paint per line —
Sap Green: PY150, PG7— and press Check palette. A paint made from several pigments is only as lightfast as its weakest one, so the report shows that weakest rating for each paint. - Keep the result. Copy report gives you a plain-text summary; Copy table and Download CSV take whatever the browse table is showing. Your pasted palette is remembered in this browser for next time.
What the ASTM numbers actually mean
ASTM International publishes specifications for artists’ paints: D4302 for oils and alkyds, D5098 for acrylics, D5067 for watercolors, and D6901 for colored pencils. Their lightfastness test (ASTM D4303) exposes paint samples to natural daylight behind glass and to filtered xenon-arc lamps, then measures how far each color moved using the CIELAB color difference, ΔE.
| Category | Color change after testing | Meaning |
|---|---|---|
| I | ΔE 4 or less | Excellent — barely measurable change |
| II | over 4, up to 8 | Very good — suitable for artists’ paint |
| III | over 8, up to 16 | Fair — visible change; not accepted in conforming artists’ paint |
| IV | over 16, up to 24 | Poor |
| V | over 24 | Very poor |
For context, a ΔE of about 2 is roughly where a careful viewer begins to see a difference between two swatches side by side. A Category III color has shifted several times that much. The specifications only allow Categories I and II in paint that claims to conform, which is why “ASTM I” on a label is worth looking for.
Two details trip people up. First, ratings belong to a pigment in a particular binder: a red can test I in oil and worse in watercolor, where a thin film of pigment sits on paper with very little binder to shield it. Second, the tests include tints mixed with white. Some pigments look fine at full strength but fade badly when thinned or lightened — alizarin crimson (PR83) is the classic example.
Reading a paint label
Take a tube called Cerulean Blue Hue with the codes PB15:3, PW6. The word hue means the paint imitates a traditional color with different pigments; here, phthalo blue and titanium white stand in for the cobalt-based genuine cerulean (PB35). Both ingredients rate ASTM I, so the paint is reliable, it just mixes differently: stronger, more transparent in thin layers, and staining. Student ranges lean on hues like this to keep prices flat; the Art Supply Comparison Tool shows where that trade-off matters and where it doesn’t.
Now take a Sap Green listed as PY150, PG7, PR101. Three pigments, all rated I, so the mixture is fine. If the yellow were a fugitive one, the green would drift toward blue as the yellow faded while the label still said “Sap Green”. That is the logic behind the palette checker: a mixture’s rating is its weakest ingredient’s rating.
Labels can also carry a manufacturer’s own scale. These map roughly onto each other:
| ASTM | Blue Wool Scale (1–8) | Winsor & Newton permanence |
|---|---|---|
| I | 7–8 | AA (extremely permanent) or A (permanent) |
| II | 6 | A |
| III | 4–5 | B (moderately durable) |
| IV–V | 1–3 | C (fugitive) |
Treat the table as a translation guide, not an exact conversion. The Blue Wool Scale, used by many European brands, rates fading against standard dyed wool cloths, and Winsor & Newton’s permanence letters also account for chemical stability, not just light.
Tips from practice
Run your own window test. Paint a strip of each color at full strength and as a thin wash or white tint, cover half with card or foil, and tape it to a sunny window for two to three months. Fugitive colors announce themselves long before that; the covered half gives you an honest comparison.
Thin layers fail first. Watercolor washes, glazes and colored-pencil layers carry far less pigment than a thick oil passage, so a color that is merely “good” in masstone can fade visibly in a glaze. Choose ASTM I for anything you plan to apply thinly.
Watch the bright pinks, violets and “opera” colors. Many of the most vivid magentas and fluorescent pinks in student ranges rely on dyes. Quinacridones (PR122, PV19, PR202) give you clean, lightfast pinks and violets instead; if you need to land on a particular shade with them, the Paint Mixing Calculator finds the closest pair and ratio.
Markers and many colored pencils are a different story. Alcohol markers are dye-based and should be considered fugitive unless the maker says otherwise. For work you sell, use lightfast pencil lines rated under ASTM D6901, or plan to scan the original and sell prints.
Keep a pigment list with every painting. Note the codes you used on the back of the canvas or in a studio log. If a collector or conservator asks years later, you can answer exactly — and you will know which tubes to replace if a color disappoints. Watercolor painters get this record almost for free: the Watercolor Mixing Chart Builder labels every chart with the same codes.
Handling cautions in the table mark pigments containing cadmium, cobalt, lead or mercury. In the US, art materials must carry chronic-hazard warnings under ASTM D4236, so read the back of the tube as well as the front.