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suspensions of inorganic pigments and extenders in drying oils prepared from vegetable oils with sufficiently high drying properties or from oily alkyd resins. Pigments include titanium dioxide, ocher, Indian red, chrome oxide, and chrome yellow. Talc, kaolin, mica, and other extenders are primarily used to economize on pigment use. Other components of oil paints are siccatives and surface-active agents. Siccatives are soluble in drying oils formed from cobalt, manganese, and lead salts. Surface-active agents are used during the preparation of the oil paints to dilute the pigments and extenders.
Two types of oil paints are produced commercially: thick-milled (pastelike) and ready-mixed (liquid). The manufacture of thick-milled oil paints involves the preparation of a homogeneous pigment paste in a mixer, followed by grinding in a mill. Ready-mixed oil paints are produced by mixing all the components in a ball and pebble mill or by diluting thick-milled paints with a drying oil. Oil paints are applied to a surface by brush, roller, or spray. The oxidative polymerization of the vegetable oils causes a film to form as the paint dries. The rate of drying and the properties of the film are dependent on the type of oil and pigment used, as well as on the drying conditions (temperature, lighting). For example, films formed at room temperature are not hard, have poor water resistance, and disintegrate upon action of alkalis. The properties of the film improve at higher drying temperatures. For example, films dried at 250°-300°C are stable in diluted alkaline solutions. Easy to use and inexpensive, oil paints are mainly used for painting walls, roofs, and other large surfaces.
In addition to all-purpose oil paints, those used in the fine arts are important. These paints are prepared by grinding pigments in bleached, refined linseed oil (sometimes with additions of walnut and sunflower oils). These oil paints are applied to primed canvas or wood.