I bought some copper/sterling bimetal from Reactive Metal Studios
(one of my favorite suppliers) and etched a design through the copper
to the sterling using ferric chloride. The design looks fine, but
whenever I use fluid that is supposed to patinate only the copper, to
highlight the design and make it stand out in comparison to the
sterlng, the fluid stains the silver as well. It doesn’t turn it as
dark as the copper, but it still turns the silver a muddy color, and
I can’t remove the patina from the silver without also removing it
from the copper.
This happens no matter what fluid I use – Brass, bronze & copper
oxidizer from Rio, or Baldwin’s Patina or Antique Patina from
Reactive (none of which are supposed to darken silver). If I use
silver black to darken the silver and not the copper, it still
darkens the copper somewhat, forcing me to buff the raised design.
Does anyone know what I could be doing wrong?