Different Ways to Prepare an Artist Canvas
Before you begin painting on a canvas, you must prepare it with sizing, gesso or another ground. These materials will seal the canvas to protect it from direct contact with oil paint, which can cause the canvas to decay. Sizing and gesso also create a nonabsorbent surface for oil painting.
Acrylic Gesso
Using a large brush, begin to apply gesso at the center of the canvas and work your way out to the edges. Don't merely skim the brush over the surface; make sure you are pressing the gesso into the fibers of the canvas. Often one layer of acrylic gesso will be sufficient, but some gessos need to be applied in two or three layers. Make sure to check your gesso's label to find out how many layers to use. If you will be preparing a lot of canvases, buy acrylic gesso in bulk; it is usually cheaper to buy gallons than smaller quantities.
Rabbit-Skin Glue and Oil Primer
Rabbit-skin glue, a traditional sizing used by Italian Renaissance painters, is much less common today, perhaps because of its more complicated preparation requirements. This glue seals the canvas and allows you to then use an oil primer rather than an acrylic primer. Rabbit skin glue can be hard to find; look for it at online art supply stores. You will have to dilute it in water, using about 2 oz. of glue to 1 liter of water. Heat the mixture in a pan until the glue dissolves and then let the glue cool. Use the glue as soon as it cools so it doesn't have time to separate from the water. Cover the canvas, making sure to press the glue into the fibers. Use oil primer or gesso on top of the glue and allow the surface to dry before you begin painting. Only oil paint, rather than acrylic, can be used on top of an oil-primed canvas.
Modeling Paste
If you tend to build your surfaces up with large quantities of oil paint, consider applying modeling paste before you begin. This will give your surface more dimension and will give the canvas more protection. Follow the procedures for acrylic gesso or rabbit-skin glue and oil primer before you apply modeling paste.
Prime Unstretched Canvas
There is no rule that says you have to stretch your canvas. Consider priming a large area of unstretched canvas to pin to a studio wall. According to the National Gallery of Australia, the French painter Pierre Bonnard painted almost exclusively on unstretched canvas, often cropping the painting to rectangular dimensions only once he felt it was complete.
