Gesso

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Gesso

Gesso ['dso] is the Italian

Italian language

Italian is a Romance languages spoken by about 63 million people as a first language, primarily in Italy. In Switzerland, Italian is one of four Linguistic geography of Switzerlands....
word for "Board chalk" (akin to the Greek word "gypsum

Gypsum

Gypsum is a very soft mineral composed of calcium sulfate dihydrate, with the chemical formula calciumsulfuroxygen4?2water....
"), and is a powdered form of the mineral

Mineral

A mineral is a naturally occurring solid formed through Geology processes that has a characteristic chemical composition, a highly ordered atomic structure, and specific physical properties....
calcium carbonate

Calcium carbonate

Calcium carbonate is a chemical compound with the chemical formula CalciumCarbonOxygen3. It is a common substance found as Rock in all parts of the world, and is the main component of seashells, snails, and eggshells....
used in art. Gesso was traditionally mixed with animal glue, usually rabbit-skin glue

Rabbit-skin glue

Rabbit-skin glue is a sizing that also acts as an adhesive. It is essentially refined rabbit collagen, and was originally used as an ingredient in traditional gesso....
, to use as an absorbent primer coat for panel painting

Panel painting

A panel painting is a painting on a panel made of wood, either a single piece, or a number of pieces joined together. Until canvas became the more popular support medium in the 16th century, it was the normal form of support for a painting not on a wall or on vellum, which was used for miniature in illuminated manuscripts and also for pa...
with tempera

Tempera

File:Duccio The-Madonna-and-Child-128.jpgTempera is a type of artist's paint and associated Art techniques and materials that were known from the classical world, where it appears to have taken over from encaustic painting and was the main medium used for panel painting and illuminated manuscripts in the Byzantine world and the Middle Ages...
paints. It is a permanent and brilliant white substrate, as long as it is used on wood or masonite

Masonite

Masonite is a type of hardboard invented by William H. Mason....
. This mixture is rather brittle and susceptible to cracking, thus making it unsuitable for priming canvas

Canvas

Canvas is an extremely heavy-duty plain weave cloth used for making sails, tents, marquees, backpacks, and other functions where sturdiness is required....
.

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Acrylic gesso

Modern acrylic "gesso" is actually a combination of calcium carbonate

Calcium carbonate

LaTeX

LaTeX is a document markup language and Word processor for the TeX typesetting program. Within the typesetting system, its name is styled as ....
, a pigment

Pigment

A pigment is a material that changes the color of light it Reflection as the result of selective color absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which the material itself emits light....
and other chemicals that ensure flexibility, and ensure long archival life. It is sold premixed for both sizing

Sizing

Sizing or size is a substance that is applied to materials as a protecting glaze, filler, or lubricant. It is used to change surface properties in papermaking, gilding, and the manufacture of textiles and fiberglass....
and priming a canvas

Canvas

Canvas is an extremely heavy-duty plain weave cloth used for making sails, tents, marquees, backpacks, and other functions where sturdiness is required....
for painting

Painting

Painting is the practice of applying paint, pigment, color or other medium to a surface . In art, the term describes both the act and the result, which is called a painting....
. While it does contain calcium carbonate (CaCO3) to increase the absorbency of the primer coat, Titanium dioxide

Titanium dioxide

Titanium dioxide, also known as titanium oxide or titania, is the naturally occurring oxide of titanium, chemical formula titaniumoxygen2....
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. Typically, a canvas should be sized prior to being gessoed, as a sizing coat will sink into the substrate to support it as opposed to a gesso coat which is just put on top of the substrate.

Acrylic gesso can be colored, either commercially by replacing the titanium white with another pigment, such as carbon black

Carbon black

Carbon black is a material produced by the incomplete combustion of heavy petroleum products such as FCC tar, coal tar, ethylene cracking tar, and a small amount from vegetable oil....
, or by the artist directly, with the addition of an acrylic paint. Acrylic gesso can be odorous, due to the presence of ammonia

Ammonia

Ammonia is a chemical compound with the chemical formula nitrogenhydrogen. It is normally encountered as a gas with a characteristic pungent odor....
and/or formaldehyde

Formaldehyde

Formaldehyde is a chemical compound with the chemical formula H2CO. It is the simplest aldehyde. Formaldehyde exists in several forms aside from H2CO: the cyclic trimer trioxane and the polymer Polyoxymethylene....
which are added in small amounts as preservatives against spoilage. Pre-gessoed canvases can be obtained commercially.

Acrylic gesso is a modern art material, and is used as a primer for oil painting

Oil painting

Oil painting is the process of painting with pigments that are bound with a medium of drying oil ? especially in early modern Europe, linseed oil....
and acrylics. Many of the solvents used in oil painting, such as turpentine

Turpentine

Turpentine is a fluid obtained by the distillation of resin obtained from trees, mainly pine trees. It is composed of terpenes, mainly the monoterpenes alpha-Pinene and beta-Pinene....
or odorless mineral spirits

Mineral spirits

Mineral Spirits, also called Stoddard solvent [CAS 8052-41-3], is a petroleum distilate commonly used as a paint thinner and mild solvent. Outside of the United States and Canada, it is referred to as white spirit....
(OMS), will leach some oil through a thin acrylic primer coat and damage the canvas underneath just as traditional hide glue sizing did. However, sufficient coverage and penetration of an absorbent support is archivally acceptable.

Although it is generally believed that it is acceptable to paint in oils over acrylic gesso, it has been stated in several painting textbooks such as "The Painter's Handbook" that it is unwise to paint in oils over acrylic gesso because--unlike time-tested alternatives such as rabbit skin glue--the oil paint will eventually delaminate from the acrylic gesso surface. This effect may not make itself manifest for several decades and then mostly affecting thick impasto. The cause for this problem is the inability of oil paint to establish both physical and chemical bonds with the acrylic base. Applied to a canvas that has been primed with rabbit-skin glue, oil paint is able to penetrate the ground (which is porous, unlike acrylic gesso) and establish a permanent bond, both chemical and physical.

Gesso and sculpture

Gesso is also used by sculptors

Sculpture

Sculpture is Three-dimensional space artwork created by shaping or combining hard and or plastic material, sound, and or text and or light, commonly Stone sculpture , metal, glass, or wood....
, to prepare the shape of the final sculpture (fused bronze) or directly as a material for sculpting. Gesso can also be used as a layer between sculptured wood and gold leaf. In this case a layer of red shellac called "assiette" is used to cover the Gesso before applying the gold. A collection of gesso sculptures is properly called a gypsotheque.