Published: Jan 2012
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BEFORE ENTERING INTO ANY DISCUSSION RELATING to pigments, it is first necessary to clearly define what is understood to be an organic pigment as opposed to a dye-stuff. In many earlier texts on color and articles concerning the use of color, the terms “pigment” and “dyestuff” are used almost interchangeably and often incorrectly. A definition of a pigment has been proposed by the Color Pigments Manufacturers Association (CPMA) in response to a request from the Toxic Substance Interagency Testing Committee. This definition was developed specifically to enable differentiation between a dyestuff and a pigment with the intention of forever ending the confusion surrounding these two terms. As such, it is worthwhile reproducing this definition in its entirety: “Pigments are colored, black, white, or fluorescent particulate organic and inorganic solids which usually are insoluble in, and essentially physically and chemically unaffected by, the vehicle or substrate in which they are incorporated. They alter appearance by selective absorption and/or by scattering of light. Pigments are usually dispersed in vehicles or substrates for application, as for instance in inks, paints, plastics, or other polymeric materials. Pigments retain a crystal or particulate structure throughout the coloration process. As a result of the physical and chemical characteristics of pigments, pigments and dyes differ in their application; when a dye is applied, it penetrates the substrate in a soluble form, after which it may or may not become insoluble. When a pigment is used to color or opacify a substrate, the finely divided insoluble solid remains throughout the coloration process.” Additionally, the older terms “lake” and “toner” may be encountered when dealing with pigments. American terminology, applied to pigments, defines a toner as an organic pigment that is free of inorganic extender pigments or carriers; as such, the pigment is unadulterated and exhibits maximum tinting capacity for the pigment type. A lake, conversely, is an organic colorant that has been combined with an inorganic substrate or extender such as barium sulfate (Blanc Fixe) or alumina. In European terminology, toners are considered to be water-soluble acid or basic dye-stuffs that are converted into insoluble pigmentary forms by appropriate precipitation with an inorganic compound. As such, Barium Lithol red (C. I. Pigment Red 49:1) and the phosphotungsto molybdic acid (PTMA)-based Rhodamine (C.I. Pigment Violet 1) are considered toners. In the coatings industry, the term “toner” may be used to refer to a secondary color that is added to alter the primary hue of the paint. The term “lake” now has an accepted definition as that used in America.
Merchak Sun Chemical Corporation, Cincinnati, OH