The gesso layers typically used in gilding are a mixture of a hide glue and an inert filler such as calcium carbonate. Since relative humidity has a dramatic influence on the mechanical and physical properties of the glue, mixtures of gessos containing the glue will be similarly affected. This paper examines some of the effects of environmental moisture on the mechanical and physical properties of rabbit skin glue alone and gesso mixtures containing this glue and calcium carbonate. The mechanical effects of an initial single relative humidity (RH) cycle is compared to the effects of several consecutive RH cycles.