prov:value
| - The color tone, the fastness to light and the fastness to washing of these dyes can markedly be improved by the presence in the positive material of salts of multivalent metals, e.g., zinc, copper, iron, cadmium, cobalt, nickel, chromium, titanium, molybdenum, or tungsten, if tetrazolium compounds are used wherein R is an aryl radical, which in its ortho position bears an electronegative group suc
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