Auxillary Products
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(Excerpts from ART HARDWARE: The Definitive Guide to Artists’ Materials, by Steven Saitzyk © 1987) A number of auxiliary products are available for use in acrylic painting. They are designed to prepare a surface for painting, to slow the drying time of the paints, or to enable the artist to create texture on a surface. Polymer Gel is a thickening agent that may be added to a polymer medium. For example, sodium polyacrylate can be added to acrylic polymer emulsions. Gels allow for an impasto style of painting with polymer paints. The more gel used, the more transparent the paint film. Gels are resistant to cracking and are excellent as adhesives for collage. An Acrylic Retarder is either a gel or an additive that evaporates without a trace. It is designed to slow the drying time of acrylic polymer emulsion paints. The recommended amount of retarder to be used varies from manufacturer to manufacturer and if specified amounts are exceeded, the paint film will not form properly. Most retarders, when mixed properly with a color, will slow the drying time to approximately three hours. This allows areas of a painting to be blended or reworked in much the same way as can be done with oil paint. Acrylic Modeling Paste is a unique product. It is a waterborne, puttylike substance that dries matte and opaque. It is an acrylic polymer medium mixed with marble dust and titanium dioxide. This product is used to build up textured surfaces and sculptured reliefs on absorbent surfaces. If it is to be applied to a flexible surface it must be mixed half and half with gel medium or cracking may result. When this paste is dry it may be carved, sanded, and painted with either waterborne or oil paints. Acrylic polymer paints may be mixed directly into it. Acrylic Polymer Gesso is not the same as the traditional gesso formulation of white pigment and chalk mixed with hide glue. Although both are designed to create a primed surface for painting, the traditional gesso can only be used on a rigid support, such as a wood panel, since it is not the least bit flexible and will crack if applied to anything that moves or bends. Acrylic polymer gesso is a combination of gypsum, or chalk, titanium dioxide, and just enough acrylic polymer medium to keep the undiluted mixture from cracking on a flexible support, such as canvas. Acrylic polymer gesso can be used to prepare any absorbent surface to receive either polymer emulsion paints or oil paints. Recent investigation seems to indicate that acrylic gesso may be more resistant to chemical attack by the pollution in city air than traditional gesso for rigid supports or the traditional combination of rabbit-skin glue and lead white for canvas supports. Today, acrylic polymer gesso has all but replaced all traditional gessos. Although acrylic polymer gesso can be applied without thinning, it is much easier to work with if it is thinned. Because it has a minimum of acrylic polymer to provide a very absorbent painting surface, it can crack if diluted only with water and applied to a flexible and highly absorbent surface. It is therefore wise to add some acrylic polymer medium whenever water is added. Excellent results can be obtained using a mixture of 25 percent polymer medium, 25 percent water, and 50 percent acrylic polymer gesso for priming canvas. Artists have reported that some brands of less expensive acrylic gesso may be more subject to cracking. The problem occurs when the gesso is not properly formulated-when it contains too much particulate matter (pigment and filler) in relation to the acrylic emulsion. As the gesso dries, the overloading of pigment prevents the acrylic resin particles from forming a complete paint film, and the resulting paint film is weak and brittle. Problems such as these teach two important lessons-read the instructions on the jar, and combine acrylic polymer gesso and acrylic polymer paint made only by the same manufacturer. (Excerpts from ART HARDWARE: The Definitive Guide to Artists’ Materials, by Steven Saitzyk © 1987) |
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