unreactive ground singlet state preventing the triplet state from participation in the degradation reactions the amounts of metal ion required to provide high photochemical stability are not highly critical and can be determined by routine experimentation having regard for this disclosure in general i prefer to employ upward of about 4 wt zinc or 9 wt sodium or both in the dye solution although greater amounts are not harmful and smaller amounts are at least partially effective the metal content should be a minimum of upwards of 2 wt for at least partial effectiveness the following examples illustrates the practice of the preferred embodiments of the invention and are not intended to serve as limitations on the scope thereof which is defined only in the appended claims this example illustrates the light instability of a tc product with negligible content of metal ions a sample of the tc product is prepared in accordance with example 1 of my u s pat no 6 086 852 incorporated herein by reference and further purified by preparative high performance liquid chromatography the total metal content of this sample is less than 0 2 wt an aliquout of this purified tc product sample is deep blue in color after standing overnight in the laboratory exposed to ambient incandescent light.