Q. From time to time I travel to tropical locations to paint in oils. Unfortunately, the humidity is high, air conditioning is non-existent and mildew is guaranteed. To keep mildew off my raw canvases I can put them out in the sun, but what could I do once I start and then finish painting?
A. Tropical climates certainly present a painter with problems of excessive heat and dampness, and youre right about the need to protect the canvas from mold growth, especially on the back, but fortunately you dont need to take any extraordinary measures to keep your canvases safe. One procedure that works well is to prime both sides of the canvas with acrylic gesso, which not only protects the canvas from mildew and mold but also reduces its response to changes in relative humidity. To do this, stretch the canvas so that it can be restretched later by allowing ample margins and driving the tacks in only partially (or using staples). Then apply two coats of acrylic gesso to the entire canvas, including the tacking margins. After thorough drying, remove the tacks and turn the canvas over on the stretcher, applying another two or three coats of gesso to the raw side so that both sides are well-coated.
Some artists get a similar result by using commercially prepared acrylic-grounded canvas and applying a new acrylic gesso ground to the back. I recommend a backing board to protect the canvas from punctures and dirt accumulation, but it should be well-ventilated by at least four 1-inch diameter holes, one in each quarter of the board, and there will still be a tendency for moisture to build up inside the backing board so the back of the canvas should be periodically checked.
A better alternative might be to paint on multimedia board that has been primed on both sides like a canvas. There are several of these lightweight boards on the market; theyre available up to 30×40 inches, they may easily be cut to size, and theyre compact for travel. Once you return from your trip, they can be mounted on a panel, the back of which should be sealed with a waterproof urethane varnish such as a solvent-based floor varnish available from most hardware stores. Use an oil or alkyd ground with a synthetic PVA sizing to isolate the multimedia board from the oil in the ground.
Finally, avoid the use of any protein materials such as rabbitskin glue because theyre prime sites for mold growth. And remember that canvases should be stored, both before and after painting, in a well-ventilated space with lots of light. Putting them in an unventilated closet is the quickest way to grow mold.
Born in Brussels, Claire Schroeven Verbiest took art classes in Belgium and in Germany before moving to the United States. She was the winner of the High Winds Medal in the American Watercolor Society’s 1999 show.