Cathy,
I’ve been doing the same sorts of things, combining the salt and
ammonia treatment with vinegar and sometimes mixing in borax flux
with heat on copper or bronze. I’ve gotten patinas that look like
they were painted by an Impressionist ! Very beautiful tones and
patterns of color.
Now then - I put a light coat of Renaissance wax on, followed by a
second coat. This seems to “fix” the patina. But the Renaissance wax
is not especially tough and has a matte finish. So, I follow the
technique that some sculpture conservators (this was at Brookgreen
Gardens in South Carolina, where I sit at the moment) taught me,
which is to finish off with Butcher’s Bowling Alley Wax. This gives
you a very tough, durable coating that will take on a nice gloss if
polished with a soft cloth. If you want to go back to a matte finish,
simply put a light coat of Renaissance wax on over top and you’re
back to the matte finish. The two waxes are compatible.
Mind you, the important thing in order not to “mess up” the patina
(since it is often powdery and fragile) is to use a soft quality
brush. I use a Kolinsky red sable watercolor brush (got plenty since
I’m a watercolorist too) which works just fine.