(under the class definition) Processes in which a compound whose color is, or would be, adversely affected by an impurity therein, is treated to chemically modify the impurity and thus improve the color.
(1) Note. Sometimes it is not economically feasible to remove an impurity from a compound which is to be used as a pigment, and so the impurity is changed to a nondetrimental form. For example, Fe2[end subscrpt]O[supscrpt]3[end supscrpt] is changed to Fe O which does not effect the color characteristics of titanium dioxide as much as Fe2O3[end subscrpt] does.
