Acrylic Emulsion Paints

[Acrylic Polymer Tempera] - Thinners, Painting Mediums,
and Additives

The acrylic polymer tempera can be thinned with plain water, but like any paint, if it is spread over too great an area by means of a thinner that evaporates into the air, it may form a defective or chalky film. If the paint is to be thinned considerably, it is preferable to use one of the acrylic polymer painting mediums sold for this purpose by the manufacturer. The medium is based on the same material as the binder and is produced as a milky white liquid that dries clear. Most companies sell two liquid mediums. One produces films of regular gloss, and another, labeled matte medium, causes the paint to dry with a flat, nonglossy appearance. The matte medium and the regular polymer medium may be mixed with each other to provide intermediate degrees of gloss. A third type of acrylic medium is sold in paste form and is usually labeled gel medium. It can be added to the acrylic polymer tempera colors to alter their brushing quality. The gel imparts a greater body or viscosity to the colors, allows heavier impasto effects, and retains more prominently the texture of the artist's brush marks. Furthermore, the colors with gel medium added dry more slowly and can be blended and worked over a longer period of time. The gel dries to a transparent glossy film that is adhesive and flexible.

Another material that can be added to acrylic tempera paints is called acrylic modeling paste. It is a puttylike compound made of marble dust and acrylic resin and can assist the painter in building up high relief areas of color. It can be used by itself or as an additive to the acrylic tempera paints, but it is somewhat inflexible and should be used on a rigid support such as a Masonite panel. If it is to be used on a stretched canvas, at least one part by volume of gel medium should be mixed with two parts by volume of modeling paste to increase the flexibility of the impasto sufficiently to prevent cracking. [p. 194]

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