Gesso

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Gesso (Italian:ˈdʒɛsːo "chalk," from the Latin gypsum, from the Greek γύψος) is a white paint mixture consisting of a binder mixed with chalk, gypsum, pigment, or any combination of these[1]. It is used in artwork as a preparation for any number of substrates such as wood panels, canvas and sculpture as a base for paint and other materials that are applied over it.

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Traditional gesso

"Gesso", also known "glue gesso" or "Italian gesso"[2] is a traditional mix of an animal glue binder, usually rabbit-skin glue, chalk, and white pigment, used to coat rigid surfaces such as wooden painting panels as an absorbent primer coat substrate for painting. Its absorbency makes it work with all painting media including water based media, different types of tempera, and oil paint. It is also used as a base on three dimensional surfaces for the application of paint or gold leaf.[3] Mixing and applying it is an art form in itself since it is usually applied extremely thin in 10 layers or more. It is a permanent and brilliant white substrate, used on wood, masonite and other surfaces. The standard hide glue mixture is rather brittle and susceptible to cracking, thus making it suitable only for rigid surfaces. For priming flexible canvas a emulsion of gesso and linseed oil, also called a "half-chalk ground", is used.[4] In Geology, Italian "Gesso" corresponds to the English "Gypsum", as it is a calcium sulphate compound (CaSO4·2H2O).

Acrylic gesso

Modern "acrylic gesso" is technically not gesso at all.[5] It is a combination of calcium carbonate with an acrylic polymer medium latex, a pigment and other chemicals that ensure flexibility, and ensure long archival life. It is sold premixed for both sizing and priming a canvas for painting. While it does contain calcium carbonate (CaCO3) 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, or substandard latex components will cause the resulting film to dry to a brittle surface susceptible to cracking.

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