Notebook, 1993-


Extenders and Stabilizers

The following materials are sometimes found in artists' paints and grounds as additives to the pigments. They are used to improve the texture or body of paints or to modify other mechanical characteristics of paints without altering their color. They are also used as extenders or adulterants to stretch expensive pigments and cheapen the color. [Kay, Reed. The Painters Guide to Studio Methods and Materials. Englewood Cliffs, NJ: Prentice-Hall, Inc., 1983. p. 18]

Aluminum Hydrate is aluminum hydroxide, a light translucent powder often used as a carrier for lake colors and as an extender for oil paints. Transparent in oil, it does not mask the yellowing of the linseed oil necessary to bind it in the paint film; therefore, oil paints containing liberal amounts of aluminum hydrate will turn yellow with age. [p. 18]

Aluminum Stearate is a white powder that forms gels with oil or turpentine. Sometimes used in small amounts to prevent the separation of pigments from binding oils, it is also added to varnishes to produce flat, nonglossy coatings. An excess amount of aluminum stearate in an oil painting produces soft, crumbly, and slow-drying films. [p. 18]

Bentonite is an American clay, sold as a powder, that gels when added to water. It is used to make pastel chalks less brittle. [p. 18]

Bole (Gilder's Clay, Armenian Bole, Red Burnish Gold Size) is a natural aluminum silicate containing iron. It is a soft native red clay, rather greasy in texture, which is used in gilding. [p. 18]

Diatomaceous Earth (Celite (Johns-Manville, Celite Division, N.Y.C., NY.), Diatomite) is silicon dioxide formed by the remains of water plants. Large deposits of the earth formed by these organisms are found in California. The lightweight granular earth, sold in the form of a fluffy powder, is often used as an aggregate to reduce the glossy appearance of paints. [p. 18.]

Kaolin (China Clay, Pipe Clay, Fuller's Earth) is hydrated aluminum silicate. Available as a fine white powder with a rather slippery oily texture, kaolin is slightly adhesive when mixed with water. The best grades are found today in native deposits in England, although the name kaolin comes from China and indicates a material from which the best white porcelain was made. It is used as a carrier for lake colors, as a filler in paints, and as a modifying material in pastels. [p. 18]

[Kay, Reed. The Painter's Guide to Studio Methods and Materials. Englewood Cliffs, NJ: Prentice-Hall, Inc., 1983.]



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