Gesso Vs Rabbit Skin Glue

I recently came across the Gamblin Art supplies site, and realized that I have been mistaken in the uses of Gessoe and sizing.  Traditional canvas sizing does not employ Traditional Gessoes as they are evidently too brittle. For most people the newer Gessos, made with Latex and other modern materials will still work on Canvas, however individuals using traditional materials should use Rabbit Skin Glue. The drawback with using Rabbit skin glue, however is that it shrinks and swells with certain humidity levels.  PVA Glue can be used in its place as it is unaffected by Humidity. Elmer's School glue is an example of PVA Glue, but there are many others.

Traditional Gesso should be used on stiff panels or boards, according the the Gamblin site. A simple homemade gesso can be created from PVA glue, water, Calcium carbonate (marble dust) or Calcium Sulfate (Gypsum) and may be whitened with Titanium dioxide.  Personally I think that using a whitener is probably not needed, as the surface will be painted over anyways.  However, if glazing in thin layers of oil, it may be desirable to have a white surface underneath to provide for glowing glazes.  

Supports may be created out of Cotton duck, Linen, Masonite, or pretty much anything else, including found objects as discussed in previous posts. I personally like a rough surface to paint on, but many artists, esp. portrait painters prefer a smoother finish. In order to get a really smooth finish, gesso should be applied in layers, with each layer allowed to dry, then sanded smooth.  This should be done until a glass smooth surface is achieved, keeping in mind that too many layers may create cracking in the finished painting.  Usually 2 or three layers is sufficient.  I personally prefer to stretch my own canvas from cotton duck.  Stretcher bars are relative inexpensive, and come in various strengths and sizes.  I've also seen other artists use heavy printed denim when money was tight to good effect,   I use a canvas stretcher on the duck to get a nice tight surface, but lighter supports such as linen should be stretched only as tight as one can get using the hand, then fastened with canvas tacks or staples. Applying too much pressure will cause the linen to warp or tear.