G’day Hans; This isn’t a recipe but a suggestion; simply anodize the
aluminium and dye it with household dyes.
Immerse the workpiece in a vessel containing pickle or sodium
sulphate solution, (sold as Glaubers Salts in a pharmacy), to act as
an electrolyte. Connect the work to the positive lead of about 6-12
volts direct current (batteries) and a piece of stainless steel to
the negative, stir occasionally Leave it for half an hour (you can
experiment with scrap aluminium) wash and then use a dye - black -
in your case obtainable from most supermarkets, or even pharmacies.
Wash the work well in hot water and dry properly. The dye should not
wash off or rub off easily, because it is attached to the thin film
of alluminium oxide produced by aluminium.
Cheers for now,
John Burgess; @John_Burgess2 of Mapua, Nelson NZ