Of all the painting media, watercolour is the most exposed. It sits transparent on paper with no protective oil or varnish film, so the pigment itself carries the whole burden of permanence. Lightfastness - a pigment's resistance to fading under light - is therefore not a footnote for watercolourists. It is the first question to ask of any colour that will be framed and displayed.
Why lightfastness matters most in watercolour
A faded oil painting usually dulls; a faded watercolour can disappear. Because the paint film is so thin and unprotected, even moderate light exposure over years can bleach a fugitive pigment to a ghost of its original colour. Work that took hours to make can be ruined in a sunny room within a decade.
The two rating scales
ASTM (used in the US) rates pigments I to V, with I and II considered excellent for artists' use. Blue Wool (used internationally) rates 1 to 8, with 7-8 considered highly permanent. For watercolour intended to last, look for ASTM I-II or Blue Wool 7-8.
How to read a lightfastness rating
A responsible manufacturer publishes the lightfastness of each individual colour, not a blanket claim for the range. Some pigments (ultramarine, the quinacridones, the iron oxides) are inherently permanent; others, including some traditional lakes and certain dyes, are not. The brand does not change the chemistry - a fugitive pigment is fugitive in any tube.
Fugitive pigments to watch for
- Traditional Alizarin Crimson (PR83) - famously fugitive; modern Quinacridone Rose (PV19) is the permanent substitute.
- Some opera and fluorescent pinks - bright but short-lived.
- Certain dye-based yellows and oranges in student ranges.
Building a permanent palette
Choose pigments rated ASTM I or II for anything that will hang on a wall. Reserve genuinely fugitive colours - if you use them at all - for sketchbooks and journals that stay closed. Our Best Watercolours guide names permanent pigments by code, and every colour in the watercolour range publishes its lightfastness so you can choose with certainty.