Gesso

"Gesso" is the Italian word for "chalk" (akin to the English 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. This mixture is rather brittle and susceptible to cracking, thus making it unsuitable for priming canvas.

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Modern acrylic "gesso" is actually a combination of calcium carbonate with an acrylic polymer medium and a pigment. It is sold premixed for both sizing and priming a canvas for painting. While it does contain calcium carbonate to increase the absorbency of the primer coat, Titanium dioxide or titanium white is often added as the whitening agent. This allows the "gesso" to remain flexible enough to use on canvas. High concentrations of calcium carbonate will cause the resulting film to dry to a brittle surface susceptible to cracking.

Italian: Italian may refer to:...

Chalk: Chalk is a soft, white, porous form of limestone composed of the mineral calcium carbonate. It is relatively resistant to erosion and slumping compared to the clays that it is usually associated with, and so forms tall steep cliffs where chalk ridges meet the sea. Chalk hills, known as chalk downlan...

Gypsum: Gypsum is a very soft mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O....