Hi,
I'll have to go to the shop and dig out the book, there are literally
hundreds of formulae for hot, cold, and in between patina processes using
many different chemicals and processes. However, for the simple blackening of
brass, Birchwood Casey Brass Black is very good. You must be absolutely sure
that the surface is TOTALLY clean. We wear new, unpowdered rubber gloves
during the cleaning to be sure that no grease and oils from the skin
contaminate the metal surface.
Even with new brass, we immerse it in gel aircraft stripper to remove
lacquer, varnish, oil, wax, etc., that may be on the metal. After thorough
wash in water, the piece is immersed in 50/50 muriatic acid/water bath to
further clean the surface. In some stubborn cases we have gone to straight
muriatic acid, being careful to avoid getting the fumes in the eyes, nose, or
mouth. Another thorough rinsing in clean running water, then dry with a clean
towel and bake at 105 degrees F for the rest of the day, and leave in the
oven overnight to cool down.
If you are going to blacken the surface, use ScotchBrite to provide a
"tooth": for the solution. Two three applications may be needed depending on
the amount of Zn, Sn, Pb, Ni, etc in the brass.
Hope this helps.
Walt
