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Abstract

The subject invention relates to a process for preparing ferriferrocyanide pigments. The process comprises (1) forming a reaction mixture containing a ferrous salt and an alkali metal ferrocyanide; (2) adding an alkaline compound to said reaction mixture in an amount sufficient to raise the pH to at least 9; (3) oxidizing the basic solution by aeration; (4) heating the solution to a temperature of from 10.degree. C. to 90.degree. C. and (5) recovering the pigment. The advantage of the process is that no significant amount of Berlin White intermediate is formed. Consequently, it is unnecessary to use sulfuric acid to dissolve the Berlin White before oxidation. Moreover, oxidation is achieved by aeration. This is cost effective and reduces the stress to the environment. The resulting pigments are useful in coloring printing ink and carbon paper.

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First Claim