GB716119A - Improvements in or relating to the colouring of aluminium and its alloys - Google Patents

Abstract

716,119. Ornamenting. UNITED ANODISING, Ltd. Feb. 14, 1952 [March 15, 1951], No. 6304/51. Addition to 645,443, [Group XXXVI]. Class 93 [Also in Group XXXVI] A brown or bronze colour is produced on aluminium having an absorbent oxide coating, for example, an anodic coating, by immersion in a solution containing a compound of iron capable in contact with the aluminium oxide of depositing ferric oxide therein and containing one or more polyhydroxy phenolic compounds having two or more hydroxyl groups attached to the benzene nucleus and also containing a suitable stabilizer; the ferric hydroxide is precipitated and toned simultaneously. Phenolic compounds containing three adjacent hydroxyl groups per benzene nucleus are preferred; suitable compounds are pyrogallic acid, gallic acid and ethyl gallate. Rufigallic acid may be used with one or more of the above. The stabilizer may be an alkali metal or ammonium salt of oxalic acid or malonic acid or an alkyl substituted malonic acid. The iron is preferably present as a compound with the acid radical of the stabilizer, but ferric chloride, nitrate, or sulphate or ferric alum may be used if desired. The proportion of iron to stabilizer in the solution should be 1-2 atoms of iron to 3 molecules of stabilizer. The proportion of iron to phenolic compound should be 1-3 atoms of iron to 1 active hydroxyl group. Thus where the phenolic compound is of low solubility, the concentration of iron in the solution must be correspondingly limited. The pH of the solution should be maintained at 4.0-7.0 and the temperature at 60-90‹C. The coating. may be sealed after colouring by immersion after rinsing in a solution containing 0.5 per cent nickel acetate at 70‹C for three minutes and transference to water at 90‹C for ten minutes.