Pigment undertone

The first relationship can be used to predict the optimum particle size of white pigments (Table 7). The second relationship explains, for example, how white pigments in gray color mixtures can produce colored undertones as a result of selective light scattering (see Section 1.3.2). 

After the color of the sample and reference pigments has been measured, color differences are usually calculated by transformation of the X, Y, and Z values into the CIELAB system to calculate color difference. Color measurement results of black and white pigments can be expressed more simply because they only amount to a determination of the relative color undertone. For this, the environment of the reference pigment is divided into eight sectors, these being filled with color names from red to violet . The octant in which the CIELAB color position of the sample is located is found by calculation. 

When colored or black systems are reduced with white pigments, an undertone is observed, which is a particle-size effect of the white pigment (see Section 1.3.1). These undertones can be conveniently expressed as CIELAB color differences. The effects can, however, also be measured by using the difference Rz — Rx between the values obtained with the blue and red tristimulus filters. The undertone measured in this way depends on the lightness, and has a maximum at Y = 41.4. The lightness of a gray paste should therefore have this value to ensure that undertone differences between white pigments are comparable [1.32], [1.33]. 

Undertone of Near-White Samples and Gray Undertones. The undertone of an almost uncolored sample is the small amount of color by which the color of a sample differs from ideal white or achromatic material. It is described by hue and chroma. The distance and direction of the CIELAB color position of the test sample (a , bf) from the achromatic position (0, 0) are used to characterize the hue. The relative undertone is expressed by the distance and direction between the CIELAB color position of the test sample (a, b%) and that of the reference pigment (ag, b ). In both cases, the distance is expressed by a figure and the direction by a color name. For standards, see Table 1 ( Hue relative of near white specimens ). Apparatus spec-... 

Figure 10. Undertone of two nearly white samples (Ti02 pigments)...

Hydrated chromium oxide has a much cleaner, bluer undertone than chromium oxide and also exhibits excellent durability and chemical resistance. Unlike chromium oxide, it is semitransparent and limited in thermal stability to about 280°C. Above 280°C, the pigment loses its water of hydration and reverts to regular chromium oxide, with the latter s duller, dirtier hue. Phthalocyanine green has largely displaced hydrated chromium oxide as a more cost-effective, much higher tinting strength alternative. 

In addition to jetness, plastics pigmented with carbon blacks typically exhibit color undertones. Undertone in black plastics appears as a distinct blue or brown-to-orange undertone, depending on the particle size of the carbon black used. In general, in full-shade, black molded applications, fine-particle-size carbon blacks impart a bluer tone. This behavior reverses itself in tints. Large-particle-size carbon blacks impart bluer undertone. Note that the effects of fillers, polymers, and dispersion can alter the typical behavior described above. Tint strength is the relative ability of the carbon black to darken a resin colored with chromatic pigments. 

Drawout n. A method of application in which the coating is applied, usually on paper, by spreading the pigment-vehicle mass evenly with a broad knife. Useful for examination of masstone, undertone, opacity, printing strength, and in some cases, fadeometer ratings of pigments. 

Lampblack - blak (1598) n. Pigment Black 6 (77266). A bulky black soot obtained from the incomplete combustion of creosote or fuel oils, of duller and less intense blackness than channel black and other carbon blacks, and having a blue undertone and a small oil content. Syn Paris black. 

Undertone color n. Color of a thin layer of pigment-vehicle mixture applied at incomplete hiding on a white background sometimes referred to as cast or under hue. The term is sometimes used to refer to the color resulting when a pigment is mixed with white, but this should more properly be called tint-tone. 

Undertone is the term used to describe the influence of a Ti02 pigment on the colour of a tinted system, resulting from the small differences in the proportion of light scattered at different wavelengths in the visible spectrum. Differences in undertone are less apparent in white compounds than in tinted compounds. 

The more negative is this value, the bluer will be the undertone of the pigment. The undertone may also be expressed as a CIE b-value measurement in a standard grey flexible compound, and compared with the b-value of a standard Ti02 in the same system. 

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