Standardization of Textile Dyes

A committee formed by specialists of dye producers has set up testing procedures for textile dyes [19]  

Relative color strength and residual color difference by reflectance measurements. 

Color Strength, Hue, Chroma [20, p. 99-105], The coloring properties of a dye are assessed by preparing a dyed test sample whose color is evaluated. This must, in principle, always be done by the human eye because color perception, being a subjective sense impression, is not accessible to direct measurement. However, with the aid of colorimetry this visual perception can be represented more or less closely by measurable quantities. Since colorimetry is an objective method and is therefore more accurate and reproducible than subjective visual assessment, it is veiy widely used today. Color is a three-dimensional quantity and must therefore be expressed by a set of three numbers (color coordinates). In practice, these are typically the values of color strength, hue, and chroma. 

Color can be described with any accuracy only in a comparative way (i.e., in terms of deviations from a standard). Although the three-dimensional color coordinates can be determined by colorimetry (as absolute values), this is in practice not sufficient to provide an exact specification. In the case of a dye, the reference is a standard dye sample provided by the producer against which all further supplies are controlled and standardized. To be used as a basis for assessment the standard sample must be extremely stable. 

To test a dye, dyed test specimen from both the sample dye and the standard are compared under conditions that are as identical as possible and assessed visually or colorimetrically and then calculated in relative terms to the standard. A widely used method to calculate color strength is a determination based on the weighted sum of the K/S values (K is the coefficient of absorption, S the coefficient of scatter), which is used in standard specifications [21], 

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