Paint Film
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(Excerpts from ART HARDWARE: The Definitive Guide to Artists’ Materials, by Steven Saitzyk © 1987) After the liquid of a polymer emulsion evaporates, such as with an acrylic polymer, a tough waterproof film forms. Although the chains formed by polymers are broken by ultraviolet light, there is such an overwhelming number of these chains that little or no visible damage occurs from exposure to indoor lighting. Visible damage can occur, however, when the emulsion is exposed to large amounts of direct sunlight outdoors, or when the emulsion has been thinned excessively before application and then exposed to direct sunlight. If a polymer emulsion is applied to a nonoily, absorbent surface, it will remain permanently attached. Although polymer films are quite flexible, there are situations where they can crack. Cracking can occur when a polymer emulsion is overloaded with particulate matter, such as additional pigment or sand, or when a significant amount of polymer is washed out of a paint mixture during the painting process. And an extremely absorbent painting ground can draw out enough polymer from a polymer paint to cause cracking. The color range of polymer paints is limited for two reasons. The first concerns pH. Alkaline-sensitive pigments cannot be used in the manufacture of acrylics because acrylic emulsions are alkaline. Acid-sensitive pigments cannot be used in vinyl paints because vinyl emulsions are acidic. The second reason is that in polymer emulsions, subtle differences between similarly colored pigments often cannot be seen and are therefore pointless to manufacture. |
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