Composition based on tungsten and chromium aqueous solutions suitable for coloring ceramic manufactured articles and relevant high temperature coloring process
Composition whereby ceramic manufactured articles, obtained by molding pressing a ceramic mixture added with 1% to 10% TiO.sub.2 by wt., are colored in shades from yellow ocher to sienna, said composition being an aqueous or hydroalcoholic solution including tungsten and chromium inorganic compounds or organic derivatives, which is applied by controlled absorption to the surface of the ceramic material before firing.
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, including (a) dissolving a carboxylic acid selected from the group consisting of acetic acid, an organic dicarboxylic acid having a general formula (COOH)--(CH.sub.2).sub.n --(COOH), where n ranges from 0 to 10, and an unsaturated, organic dicarboxylic acid in water at a temperature ranging from 40 to 60.degree. 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 and at a temperature 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; and (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.
