WHAT IS PAINT?
A paint is a suspension of pigments and additives intended to color or protect a surface. A pigment is fine powder that is insoluble in the medium in which it is dispersed; that is, the granules do not dissolve and remain intact and are dispersed evenly across the surface, as shown in Figure 1. Pigments are intended to color and/or cover a surface; they may be organic, inorganic, or a mixture. The additives in paint come in a dizzying variety but have some constants. The binder is that portion of the coating, other than the pigment, that allows the pigment to be distrib uted across the surface. The term vehicle typically refers to the solvents, resins, and other additives that form a continuous film, binding the pigment to the surface. If “binder” and “vehicle” sound similar, they are sometimes used interchangeably in the coatings industry and the forensic laboratory. Solvents dissolve the binder and give the paint a suitable consistency for application (brushing, spraying, etc.). Once the paint has been applied, the solvent and many of the additives evaporate; a hard polymer film (the binder) containing the dispersed pigment remains to cover and seal the surface (see Table 16.1). Paints can be divided into four major categories. The first is architectural paints, sometimes called household paints, and are those coatings most often found in resi dences and businesses. Product coatings, those applied in the process of manufacturing products including automobiles, are the second major category. Because automobiles play a central role in society and, therefore, in crime, much of this chapter will focus on the paints and coatings from the automotive manufacturing industry. The third kind, special-purpose coatings, fulfil some specific need beyond protection or aesthetic improvement, such as skid resistance, water proofing, or luminescence (as on the dials of wristwatches). Finally, art paints are occasionally encountered in forgery cases. Modern art paints are similar in many respects to architectural paints, but many artists formulate their own paints, leading to potentially unique sources (see Figure 2). See “In More Detail: Coating Definitions” for additional information regarding coatings.
FIGURE 1 Paints contain pigments, fine powders that do not dissolve but are dispersed evenly across the surface. Pigments are intended to color and/or cover a surface; they may be organic, inorganic, or a mixture.
FIGURE 2 Modern art paints are mass-produced, but many artists formulate their own paints. The application process for art paints is obviously more varied and unstructured than for product coatings.
