No Regrets: Lightfastness, Pigments, and How to Buy Paints Without Regret
Let’s talk about lightfastness so you buy the right paint for you, without regrets.
Watercolor pigments react to light differently depending on their chemical makeup. UV light (mostly from sunlight, but also prolonged indoor lighting) can break down certain pigments over time, causing fading or color shifts. Watercolor paint companies usually report how light fast their paints and pigments are, and that’s where ASTM lightfastness ratings come in.
ASTM ratings (the short, useful version)
In general the lower the number, the more stable the pigment. A I on the scale usually means that the pigment will last until you’re dead enough to have your own gallery room in a museum. A IV on the scale, that might be gone before your sister’s kids are old enough to appreciate your work
ASTM I – Excellent lightfastness (very stable), recommended for professional work (equivalent to 7-8 on the Blue Wool Scale).
ASTM II – Very good lightfastness, lightfast under normal museum conditions (approx. 100 years)
ASTM III – Fair (noticeable fading over time), colors may fade within 50-75 years.
ASTM IV & V – Poor to very poor (fugitive), pigments fade quickly (15-20 years or less).
Essentially: If you’re painting for joy, studies, or sketchbooks, any of these can be fine. If you’re painting something meant to last—originals, gifts, commissions—you’ll want to lean heavily toward ASTM I and II.
Student vs professional paints
Lightfastness is one of the (potentially few) reasons in the price difference between student grade and professional paints. There is no shame in using student grade paints - it’s a great way to experiment and play with the medium before committing to more expensive supplies. However, it’s good to keep in mind:
Student-grade paints often rely on dyes or less stable pigments to keep costs down
Professional paints use higher-quality pigments, higher pigment loads, and better testing
That doesn’t mean student paints are “bad.” It means they’re not designed with longevity as the top priority and that’s ok.
Hue colors vs single-pigment paints
This one point took me a while to work out. Essentially:
Single-pigment paints are usually more predictable, easier to mix, and often more lightfast (though not always)
Hue paints are blends created to imitate another pigment (sometimes discontinued or toxic ones - I’m looking at you cadmium…)
Some hues are excellent. Some are… not. The only way to know is to check the pigment numbers and ratings.
How to buy smarter (without becoming obsessive)
Check the pigment number(s), not just the color name. this is usually available on the company’s website
Look for ASTM I or II if permanence matters
Be cautious with neons, bright pinks, and some purples - these hues are notoriously fugitive.
Know that you don’t have to throw out all your paints that have a high ASTM score, but make sure you remember them, and maybe don’t use them for items you intend to passed down as heirlooms (or hung in galleries a century after you die).
If you want a practical buying reference that doesn’t require spreadsheets, I made this specifically for working artists: use this when late night shopping for paints, or when you’re in the store and don’t want to comb through a thousand websites to find out whether that awesome new pink is lightfast or not. Basically, I developed the tool I wish existed when I was standing in the art store aisle, Googling pigment codes on my phone. So may your journey into lightfastness be less convoluted than mine.