"Gesso" ['ʒɛsːo] is the Italian word for "Board chalk" (akin to the Greek word "gypsum"), and is a powdered form of the mineral calcium carbonate used in art. Gesso was traditionally mixed with animal glue, usually rabbit-skin glue, to use as an absorbent primer coat for panel painting with tempera paints. It is a permanent and brilliant white substrate, as long as it is used on wood or masonite. This mixture is rather brittle and susceptible to cracking, thus making it unsuitable for priming canvas. In Geology, Italian "Gesso" corresponds to the English "Gypsum", as it is a calcium sulphate compound (CaSO4·2H2O).