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White and Yellow IndicesCertain industries, such as paint, textiles and paper manufacturing, evaluate their materials and products based on standards of whiteness. Typically, this whiteness index is a preference rating for how white a material should appear, be it photographic and printing paper or plastics. In some instances, a manufacturer may want to judge the yellowness or tint of a material. This is done to determine how much that object’s color departs from a preferred white toward a bluish tint.The effect of whiteness or yellowness can be significant, for example, when printing inks or dyes on paper. A blue ink printed on a highly-rated white stock will look different than the same ink printed on newsprint or another low-rated stock. The American Standards Test Methods (ASTM) has defined whiteness and yellowness indices. The E313 whiteness index is used for measuring near-white, opaque materials such as paper, paint and plastic. In fact, this index can be used for any material whose color appears white. The ASTM’s E313 yellowness index is used to determine the degree to which a sample’s color shifts away from an ideal white. The D1925 yellowness index is used for measuring plastics
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