The following methods are designed for the evaluation of dyes used for coloring paper in terms of a preselected dye referred to as the standard dye. These methods are most suited for the evaluation of dyes within a laboratory, since variations in pulps, water conditions, pH, and the observer will influence a correlation of data between laboratories. Method A is for soluble dyes and applies to dyes to be used solely for calender staining and other types of surface coloring. Method B is for soluble and insoluble colorants intended for beater applications.
Some acid dyes, e.g., Acid Yellow 23, Acid Yellow 36, and Acid Blue 9, cannot be evaluated by the beater dying method. However, the other acid dyes, basic dyes, and direct dyes may be evaluated by this method.
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