Some artists have had the experience of opening their watercolor palettes, anticipating a productive painting session ahead, only to find fuzzy grey mounds of mold growing on some of the pigments. Several of my students approached me, palette in hand, asking for a remedy. And so this blog post was born…
The grey and white molds that you might see on the paint pigments are fungus spores. Spores like these will grow and flourish provided these four conditions are met: darkness, warmth, moisture and a compatible substance to call home. If spores can find a closed palette, freshly misted with water, kept in a warm room, it is possible for growth. In this case, the spores are embedding in the gum arabic. Gum arabic is the sap from the acacia tree; it is used as a natural binding agent for most professional grade watercolor paints, allowing all the parts of the paint (like pigment, water, and other additives) to combine easily.
Nowadays, most professional grade paint also includes an antifungal additive in the mixture; often this is enough to circumvent the mold problem. However, some artists purposely try to interfere with the mold process by letting their paints dry well, leaving off the palette covers, or storing their palettes in a cool place, such as the refrigerator. Those who regularly follow these practices are often convinced that they are beating the mold problem.
Occasionally, molds will grow no matter what measures an artist tries. What should be done then? Some painters have said to mix the mold up with the paint and use it that way. This is not a good choice, as molds can alter the colors, be transferred on your brushes and grow on your painting. Once molds have sprouted on a painting, only a professional fine arts conservationist can alleviate the problem.
Others have suggested washing your palette with an anti-mold liquid. White vinegar has been offered, though most would say that vinegar is more destructive than beneficial to the paint. Another artist proposes to use a small dab of Pine-Sol on a paper towel to clean out his pan wells periodically, though the effect of Pine-Sol on paint pigments is not clear. Finally, other painters have written about using either denatured alcohol or distilled water to clean the affected paint wells, neither of which are proven treatments.
Winsor & Newton suggests instead that the affected paint wells be cleaned out thoroughly and washed with a diluted solution of Dettol liquid. Dettol is a topical antiseptic disinfectant that is gentle to your paint pigments.
So, if the dreaded molds pop up on your palette, try the Dettol liquid. I also welcome any other solutions that you have might have tried to either prevent or rid mold from occurring.