Published: Jan 2012
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BROADLY SPEAKING, COLORED INORGANIC PIG-ments all fall into one of four groups: lead chromates, metal oxides, sulfides, or sulfoselenides with a few miscellaneous pigments that do not fit into one of these classes such as cobalt blue, ultramarine blue, iron blue, and bismuth vanadate yellow. This chapter describes the chemistry, manufacture, and properties of each of these classes of inorganic pigments. Inorganic whites such as zinc oxide, titanium dioxide, lithopone, and zinc sulfide, while pigmentary in nature and most definitely a part of the coatings industry, fall outside of the scope of this chapter and are discussed elsewhere in this manual. By chemistry, inorganic pigments can be subdivided as shown in Table 1. In addition to the inorganic pigments listed in Table 1, there also exist a series of pigments classed as mixed metal oxides (MMOs); for example, zinc iron chromite brown (PBr 33), cobalt chromite green (PG 26), cobalt titanate green (PG 50), and cobalt aluminate blue (PB 28 and PB 36). Currently, these mixtures are also referred to as complex inorganic colored pigments (CICP). Often CICP and MMO terminology are used interchangeably, but CICP indicates the pigment is colored. These types of inorganic pigments are sometimes also called ceramic colors because of their widespread use in the ceramics industry. Since they are covered in the next chapter of this book, no additional consideration will be given to these colors in this chapter. Before going further into this chapter, the reader is directed to Chapter 21 for an explanation of the “Colour Index” and the description of pigments, both inorganic and organic, that has become part of a global understanding with respect to pigment nomenclature. Transparent iron oxide pigments are finding increasing importance for automotive  and wood  coatings as well as other coating end use areas. These nano-size (average size less than 0.1 μm)  pigments are available in various colors, such as yellow, red, green, blue, black, and brown. They provide color with transparency, durability, ultraviolet radiation protection, heat resistance, and improved transparency that accentuates particular coating effects. These interesting pigments are solid materials that achieve their transparency through their extremely small size and shape. They will be mentioned in some, but not in all, of the color classifications given below.
Lewis, Peter A.
Director, Sun Chemical Corporation, Cincinnati, OH