Climate Control

Q. I paint watercolors in my basement, and I’ve discovered a dark substance growing in my yellow paint. What’s the ideal humidity level for a watercolor studio and for leaving my palette open?
Beverly R. Silva
Warwick, RI

A Your studio is a fine breeding ground for mold growth: damp, cool and probably dark most of the day. That’s probably mold growing on your paint, and it’s likely to affect all your other paints. It will affect any object that remains damp and can absorb the mold spores, including your watercolor papers, which probably have an organic sizing.

Conservators often use a fumigant to get rid of mold on a watercolor paper, but I wouldn’t recommend that to a nonprofessional. A simple fix is to expose everything to a few days of warm sunlight; then you can brush off the mold dust that remains and wipe down your furniture with a damp rag and let it dry again. Brush off the papers, too. That will clean all but the paints, which you’ll unfortunately have to discard.

A damp basement just isn’t the best place for a watercolor studio, even with a dehumidifier. Central air conditioning in your basement (both supply and return air) would help, however, because air-conditioned air is quite dry. It’s not so much the humidity that’s the problem, but the humidity plus the temperature. Museums like to keep their collections at about 72? F and 50-60 percent relative humidity, so an ideal studio might shoot for these values. If possible, I’d suggest you use a room on the main floor or second floor such as a dining room or spare bedroom and save the basement for something else. In any case, I’d always cover the palette at the end of the day no matter what the environment, if only to keep dust off the paints.

From Winston S. Churchill’s essay “Painting as a Pastime” (Charles Scribner’s Sons). Churchill was an active oil painter in his later years.

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