suspensions of inorganic and organic pigments in water solutions of film-forming substances, such as cellulose ethers, polyvinyl alcohol, starch, casein, and animal glues. Besides the pigment and the film-forming substance (the content of the latter in glue colors is 3–6 percent), glue colors contain additives, such as chalk, kaolin, or gypsum. The colors are usually prepared immediately before use. Preparation involves mixing the glue (the water solution containing the film-forming substance) with the pigment (the concentrated suspension of the pigment in water). The glue colors are applied with a brush, roller, or sprayer to concrete, brick, plaster, or wood surfaces, which have been first covered with a ground (copper sulfate, lead sulfate, or potash alum).
Coatings of glue colors are porous and are usually not water-resistant; they are either mat or have a silky luster. Glue colors have great decorative possibilities. Unlike coatings of enamel or oil paints, coatings made from glue colors do not prevent the evaporation of moisture from a painted surface such as wet plaster. Glue colors are used in the decoration of civic and industrial buildings. Casein colors, which withstand weathering, are used to paint decorative details on the facades of concrete, brick, and plaster buildings. Casein coatings last four or five years and are washable.