Traditional organic sizing material, used for centuries to prepare canvas for oil priming. Prevents direct contact of the oil primer with the fabric. Rabbitskin Glue is hygroscopic; this tendency to absorb atmospheric humidity leads many to believe that Rabbitskin glue is the culprit for many cracked oil paintings. Many others feel that linseed oil may be more of a factor. If using this traditional method, the latest recommendation is to apply a thin, single coat.
Rabbit skin glue is a dry, granular powder and must be dissolved in warm water. The general rule of thumb is to add 2-3/4 oz of glue to one quart of cold water and allow this mixture to soak overnight so that the glue can absorb the water. The mixture is then heated until all of the glue is dissolved. Do not boil the mixture, boiling darkens the mixture and alters the property of the size. To prevent boiling, use a double pot. The glue is then allowed to cool. After cooling the glue will look like jelly and must be tested for strength. Place two fingers into the gel and spread them observing the fissure created. The sides of the crack should be rough or granular if they are smooth the mixture is too strong and more water must be added to weaken the mixture.