Size crystals or powder mixed with water produce a gelatinous solution which forms the binder for gesso. Glue size added to plaster retards the drying process, giving the plaster a longer working time. Rabbit skin is a source for glue size traditionally used in preparing a ground for oil painting.Related resource: Chalkboard has information about using glue size. Chalkboard is produced by Ralph Larmann, a member of the art faculty at the University of Evansville, IN. Also see adhesion, adhesive, and cleavage.