Art Terms Glossary beginning with G

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Galena: A gray metallic-like mineral composed of lead sulfide. When crushed, it forms a black powder.
Gelatin dry plate negative: Distinguished from the wet collodion negative and thedry collodion negative, the gelatin dry plate negative refers to thin plates of sheet glass coated with a gelatin emulsion made light-sensitive by silver salts. The first really practical dry plate negatives were invented in 1871 by Richard Leach Maddox and, following rapid improvements, were the most common type of negative in the mid-1880s. Dry plate negatives could be purchased precut for individual cameras, were more sensitive to light, and freed the photographer from an on-site darkroom and the messy last-minute chemical preparations of the wet collodion negative. The ease and popularity of the gelatin dry plate negative was eventually surpassed by that of the gelatin silver paper negative and the gelatin silver negative on celluloid roll-film, introduced in the late 1880s.
Gelatin silver print: The generic name for the common black-and-white photograph. The process has been the main photographic printing process since its introduction in the late 1880s. Paper is coated with an emulsion of light-sensitive silver halide in gelatin. To produce a print, the paper is exposed under a negative, either by contact-printing or through an enlarger, then chemically developed, stopped, fixed, and dried. Gelatin silver prints are normally black-and-white, although they can be toned with various compounds or minerals to produce a wide range of hues. In addition, various commercial papers will also impart warm or cool tones to the black-and-white print. A variation of the gelatin silver print, the silver bromide print is printed on a commercial paper with a bromide silver emulsion. This chemical process, available in the 1880s, was used for contact prints or enlargements by artificial light. Bromide prints have a baryta layer, a porous substance that produces tinted or clear white highlights. Usually toned with copper, these prints range from reddish-purple, brown, or slate to warm blacks. Chloro-bromide prints are still another variation of the gelatin silver print. First introduced around 1883, they are printed on chloro-bromide paper with an emulsion containing both silver chloride and silver bromide, producing a warm, black-toned, sharp image. Chloro-bromide prints were often toned different colors, including red, blue, or purple and were favored by pictorialist photographers.
Gesso: A paste prepared with size or glue and spread upon a surface to fit it for painting or gilding.
Gilding: Decorating with thin gold overlay.
Glass: A solid usually containing silica. Glass is formed by combining silica with fluxes (soda or salts) and stabilizers (lime or calcium oxide), that melt upon heating and cool to form a non-crystalline solid. Glass in ancient Egypt is defined as a soda-lime-silicate, and was made with the same raw materials used in faience and frit production.
Gloss: A commentary on a text, in smaller script in the margins or between the lines.
Gold leaf: A sheet of gold varying from four to five millionths of an inch in thickness that is used for gilding.
Gospel Book: Liturgical book containing the complete text of the Gospels of Sts. Matthew, Mark, Luke, and John. Used on the medieval altar in conjunction with the sacramentary, but after the eighth century they were partially replaced by evangelaries.
Gouache: Also referred to as bodycolor or opaque watercolor, gouache is a type of watercolor made opaque by the addition of white pigment or chalk used with a binding agent such as gum arabic. It has a matte finish, as we see in the strokes of gouache on this masterpiece by Picasso.
Gradual: Liturgical book containing the noted music and chants for the Mass sung by the choir in response to the celebrant.
Graphite: A crystalline form of carbon that can be sharpened into a stick and used for drawing. Although known since the 1500s, graphite did not become common in drawings until the 1700s. Graphite is generally grayer and smoother than black chalk or charcoal, and produces a line with a soft metallic sheen visible in raking light. Early on, graphite was confused with lead and is still today commonly referred to as lead, lead pencil, or simply pencil.
Gregory: Christian saint and one of the four Latin Fathers of the Church (along with Ambrose, Augustine, and Jerome).
Ground: The first layer of a painting applied to a wood panel or canvas. For wood panels the ground layer was generally a mixture of chalk and animal glue to create a smooth surface to paint upon. The ground on canvas paintings is often lead white, sometimes tinted various colors.
Gum Arabic: The natural secretion of the acacia tree which is used as a binding agent in many liquid media. It improves the bonding properties of the ingredients in inks and watercolors, enabling them to stick to paper, and it helps to maintain a stable dispersion of pigment particles in water as the film of wash dries.
Gum bichromate print: A print made with a technique that relies on a coating of pigmented gum arabic and potassium or ammonium bichromate, which allows the photographer to manipulate the printed image during development. The coating is brushed on a piece of drawing paper. When it is dry, a negative is placed on top of the paper and exposed to light. A viscous and light-sensitive material, gum bichromate does not respond to light by darkening, as silver compounds do, but by hardening. The amount of light striking an area determines the hardness of the gum arabic coating in that area. After exposure, the print is washed thoroughly in warm water, creating dark areas where the gum arabic has become hard and light-toned areas where it washed off. The photographer can further manipulate the image by removing more pigmented gum arabic with brushes or a stream of water during the washing stage. A prototype of the gum bichromate print, using pigment and gum arabic with potassium dichromate, was exhibited in 1858 by the Englishman John Pouncy, but the technique was not fully developed until the last decade of the century. It was popular with photographers until the 1920s.
Gum platinum print: A print that has a layer of gum bichromate printed in registration over an initial platinum print.
Gypsograph: A relief technique where the plate is made of hardened plaster.
Gypsum: A soft, transparent, mineral composed of hydrated calcium sulfate. Historically gypsum was used for carvings and as a paint pigment or ground. Burnt gypsum is commonly known as plaster of Paris.