There are basically two methods that are used for priming canvas. One, the traditional way, is with an oil base primer and the other way is with an acrylic primer. What you might consider is that the acrylic priming method seems to be easier. Also, you can paint on this base with either oils or acrylics. You should never paint acrylics over oil.
The Oil Base Primer
This is the more traditional method of priming canvas, if you choose. So, with linen or canvas it is necessary to size the stretched material to protect it from the acids and minerals that are in the paint. There are to sizes that are used; rabbit skin glue and gelatin.
Rabbit Skin Glue
Using one ounce of rabbit skin glue, we start by pounding the chunks into very small pieces with a hammer. Be sure to wrap the glue in something to keep it from flying about. Place the broken pieces of glue into a quart size or larger container. Then just barely cover with water, and let soak over night.
Slowly pour one pint of boiling water over the softened glue, a little at a time, stirring until the glue is completely dissolved and mixed with the water. You can place the pan of glue in a pot of boiling water and reheat to keep it thin. Never boil the glue!
The glue sizes do not keep well so, I suggest that you have more than one canvas ready for priming, and or mixing a small amount only enough to do the job.
Place your stretched canvas on a table protected by layers of papers or some other materials. Then, begin laying on the first coat of warm glue. Start at the edges first. You can use any house painters brush. Proceed laying on the glue, making sure to overlap and crisscross the brush strokes.
Hold the canvas up to light to check for pinholes or lightly covered areas. Also check for and remove any brush hairs that may have been shed on the canvas. Let your canvas dry well; a day or two is best, to make sure it is completely dry.
Lightly sand the canvas, taking care not to damage the fibers. Apply a second coat of size.
You can also apply the size cold. Pour the jellied size onto the middle of the canvas and spread with a spatula or broad palette knife. Again, always make sure you get complete coverage with no pinholes.
Gelatin Glue Size
Gelatin glue size (or Gelatine) is used in much the same manner as the rabbit skin glue for priming canvas. Ordinary household gelatin, such as is used for making deserts is quite often used. Mix 2 table spoons or 1 oz. with one pint of hot water. stir until dissolved. Again: Do not boil.
A Test of Your Sizing
Your sizing should jell when it cools to room temperature. If it remains liquid at temperatures below 60 degrees F, then you should add up to 1/2 ounce of glue or gelatin to the solution. If this does not remedy the solution, then it should be discarded and thrown away. Gelatine for priming canvas, (if you can find it), should be used at 3/4 ounce to one pint of water for best results.
Applying The Primer
When the sizing is completely dry you can prime the canvas. Most oil primers will be quite thick, so you may have to thin it down some. White Lead is considered to be the best. Now, add your solvent or turpentine in small amounts until you get it creamy smooth. You do not want to thin this too much as too much thinner will break down the binder. No more than 1 part thinner to 2 parts primer! Spread this with brush or spatula. Let this priming dry 24 hours before applying a second coat. The same for a third coat.
Priming Canvas With Acrylic
This is another way of preparing your canvas for painting. It is much simpler and less bothersome You should prime with three coats. I recommend thinning the first coat some with no more than 1 part water to 2 parts gesso. Another option is to apply a regular acrylic sizing as the first coat.