Bill Martin's Guide to Oil Painting
Most Oil Paintings Are on Canvas
CANVAS is the traditional surface for oil paintings. Although oil paint can be used on most non-porous surfaces the texture and flexibility of a stretched canvas is best. Many canvas surfaces are available including canvas-textured paper, canvas glued to heavy board, primed canvas in a roll and pre-stretched canvases. In ALL cases the surface should be primed or re-primed with GESSO (See GESSO). A gesso that has a neutral gray tone is preferred so the light values are more easily seen. (Acrylic paint will tone the gesso) If you prefer to use the gesso white, the canvas may later be toned with a thin coat of oil paint.
Stretching Your Own Canvas
If you need a special size canvas, just want to make your own canvases you can easily build them yourself. First all canvas is artist's canvas, whether it's from an art store, an upholsterer, a sail maker, awning maker or a fabric store. The weight of the canvas used for paintings is number10 or number12 (about the weight of denim jeans).
To stretch the canvas a wooden frame is used. For small canvases up to 18" x 24" commercial stretcher bars (A) may be used. For larger sizes 1" x 2" fir stretchers (B) are used. 1"x 2" fir boards are available from lumber sellers. You'll have to cut them and nail them up yourself.
The size of the canvas (B) here is to be 24" x 30." The short bars are 22 ½" to allow for the overlap of the longer bars. Plus there is a center brace. The corners are braced with thin triangular plywood.
The canvas should be 6" wider and longer than the stretcher frame.
The canvas is stretched and tacked to the middle of the four sides using a staple gun or upholsterer's tacks and a hammer. Then it's stretched and stapled toward the corners and the excess is trimmed. If you are using PRE-PRIMED canvas you'll need CANVAS PLIERS to stretch it tight enough. Sizing or gesso won't tighten it further.
(A) The porous canvas must now be sealed (or sized). The traditional material for this is RABBIT SKIN GLUE. The glue comes as dry crystals. One tablespoon of glue is added to each cup of water and cooked (not boiled) until smooth. The glue is applied to the horizontal canvas while still hot. The glue will tighten and seal the canvas. Let it dry overnight. (Don't use the glue on pre-primed canvas. It doesn't need it.)
(B) GESSO is applied when the glue is dry. This further seals the canvas and provides an agreeable surface for the oil paint. This particular gesso was toned with a mixture of red-violet and yellow-green acrylic.
When dry the canvas may then be lightly sanded to remove any rough fibers remaining. Multiple coats of gesso may be applied if desired. Gesso may be thinned with water to reduce brush strokes. The canvas is now ready to be a painting.