Q. What do conservators recommend you do with the back of a canvas painting? Im wondering whether I should varnish it, gesso it or just leave it raw.
A. I recommend that you dont coat the back of your cotton or linen support—to do so might cause structural problems later on. If you want to protect the back of the support, however, there are two ways to do so.
The first way is to cover the back of the support with a piece of stiff cardboard. Use screws to attach the cardboard to the rear of the stretcher bars or strainer (a strainer is a homemade auxiliary support with rigid corners). Using this covering will inhibit the deposit of dust and debris on the back of the support—especially at the lower edges—and will also slow down the fabrics movement in response to changes in temperature and relative humidity. Doing this is a good idea for any kind of paint on fabric supports, but is especially good for oil paintings; they grow more inflexible as they age and can crack if they expand and contract too much.
You could also solve the problems of losing flexibility and collecting debris by using a panel stretcher. Assemble your stretcher strips in the usual way and then tack a piece of ?-inch plywood on the back, cut to fit the stretchers exactly, using small brads. Stretch the cotton duck or linen over this assembly and then prime and paint as usual.
Mark Gottsegen is an associate professor of art at the University of North CarolinaGreensboro and chair of ASTM Internationals subcommittee on artists materials.