Use of a colorant solution containing a stable, at least partially neutralized chromium (III) coordination compound for coloring unglazed ceramic

A process for coloring an unglazed ceramic with an aqueous colorant solution containing a chromium (III) coordination compound which is at least partially neutralized and stable, comprising:

• a. dissolving a carboxylic acid selected from the group consisting of:
• acetic acid, and
• an organic dicarboxylic acid having a general formula
• (COOH)—(CH2)n—(COOH), where n ranges from 0 to 10,
• in water at a temperature ranging from 40 to 60° C. to provide an aqueous solution of a carboxylic acid;
• b. adding a chromium (III) compound to the aqueous solution of a carboxylic acid while stirring for a time of up to about 30 minutes and at a temperature up to 95° C. effective for reaction to form an aqueous solution containing a chromium (III) coordination compound;
• c. filtering the aqueous solution containing the chromium (III) coordination compound to provide a filtered aqueous solution;
• d. adjusting pH of the filtered aqueous solution to a pH ranging from 3 to 6.5 by addition of one of alkali hydroxide or ammonia to provide the aqueous colorant solution containing a chromium (III) coordination compound which is at least partially neutralized, which is stable, and which has a chromium content ranging from 5 to 10% by weight;
• and applying the aqueous colorant solution to the unglazed ceramic to color the unglazed ceramic.