Improvements in processes for coloring anodized aluminum and/or aluminum alloys

A process for coloring oxide layers on anodized aluminum or aluminum alloys comprising treating the anodized aluminum or aluminum alloy with a water soluble acidic composition a Sn(II) electrolyte and a stabilizing agent according to Formula I:

• ##STR3## wherein each substituent R.sub.1 to R.sub.10 which are not hydrogen are selected from one of the groups consisting of:
• a) one or two --COOM;
• b) one or two --SO.sub.3 M;
• c) one or two --NH.sub.2 and one or two --COOM, and
• d) one or two --NH.sub.2 and one or two --SO.sub.3 M
• wherein
• R.sub.11 is hydrogen, C.sub.1-4 alkyl, .beta. to .omega.-hydroxy-C.sub.1-4 alkyl, phenyl or (B--O).sub.n R.sub.12, wherein each B, independently is --C.sub.2 H.sub.4 --, --C.sub.3 H.sub.6 -- or C.sub.4 H.sub.8 --,
• n is from 1-20 inclusive;
• R.sub.12 is H, --SO.sub.3 M or --CH.sub.2 COOM;
• and,
• M is hydrogen or the equivalent of a cation;
• or a mixture of said compounds.

A stabilized electrolytic composition comprising

• a) Sn(II) electrolytes;
• and
• b) a stabilizing agent which is one or more compounds of the formula:
• ##STR4## wherein the R.sub.1 to R.sub.10 which are not hydrogen are selected from one of the groups consisting of:
• a) one or two --COOM;
• b) one or two --SO.sub.3 M;
• c) one or two --NH.sub.2 and one or two --COOM;
• and
• d) one or two --NH.sub.2 and one or two --SO.sub.3 M,
• wherein M is hydrogen or the equivalent of a cation, in an aqueous solution.

A stabilizing electrolytic composition comprising:

• a) Sn(II) electrolytes;
• and
• b) a stabilizing agent selected from the group consisting of:
• 4-amino-diphenylamine-2-carboxylic acid,
• diphenylamine-4-sulfonic acid,
• 2-amino-diphenylamine-4-sulfonic acid,
• 4-amino-diphenylamine-2-sulfonic acid,
• 4,4'-diamino-diphenylamine-2-sulfonic acid,
• 4'-amino-4-nitrodiphenylamine-2-sulfonic acid,
• 1-amino-2,4-di(phenylamino)benzene-5-sulfonic acid, and
• mixtures thereof;
• in an aqueous solution.