Moldy Watercolors

Q. Is watercolor paint that has mold on it still OK to use? I’m assuming that once the image is painted and dry, the mold or fungus would be inactive. Is this true?
Pete Muller
Quartz Hill, CA

A. I don’t think it’s a good idea to use moldy watercolor paints. There’s a strong possibility that the mold will spread to your other color mixtures and eventually infect the entire painting. I know a watercolorist who fixes this problem by thoroughly washing the mold off the surface of his affected pans of color with plain water and then using the paint. He says he’s never had mold on his paintings. Another solution is to first wash the paint surface with a dribble of water, then lightly wipe the surface again with a rag dampened with denatured alcohol to kill the mold spores before painting.

Of course, you could have a conservator chemically treat mold on a painting using a disinfectant that kills the mold. But mold can easily reappear given the right conditions: darkness and too much humidity. Sometimes you can kill mold by exposing the painting to warm sunlight for a few days, but then you run the risk of fading some of your pigments. So it’s best to try to prevent any mold or mildew in the first place.

The best way to prevent mold is to be sure that your pans of paint are completely dry before you close your kit. You can also add a small amount of denatured alcohol (say, half a teaspoon in a pint of water) to your rinse water to help kill active spores. Another possibility is that the water you’re using could contain some organic material that promotes mold growth. If you think that might be the source of your problem, try using distilled water for thinning your paints.

Mark Gottsegen is an associate professor of art at the University of North Carolina at Greensboro and chair of the American Society for Testing and Materials subcommittee on Artists’ Paints and Related Materials.