A white fluid or plastic coating material made by mixing chalk or whiting with a glue solution or, occasionally, casein. Early gesso was made from parchment glue and slaked plaster of Paris~ modern gesso uses rabbitskin glue and precipitated chalk or whiting. The word gesso is Italian, and derives from gypsum, from which plaster of Paris is made. However manufacturers in recent years have applied the term to polymer primers, which are entirely different from gesso in composition and cannot be used as a substitute for it.