Hasn't anyone else heard of depletion gilding? I posted two
replies to this thread referring to pre-Columbian tumbago
(gold/copper alloys that were treated to remove the copper from
the surface parts and leave a gold-rich burnished layer) and the
theory that the Western ancients also did this, but they don't
seem to have appeared. Charles Lewton-Brain does a paper on it:
I’ve heard of it and I’ve read Charles’s paper on it. When
silversmiths “raise the fire coat” they are depletion gilding.
For those that are not familiar with it, it works like this. Heat
the finished silver and quench hot. Do this five or more times.
The goal is to have a dead white surface. This means that the
copper has been removed from the copper/silver alloy called
sterling.This surface can be polished with soft copper brush
using water and detergant.