I recently saw the gold show from Sitio Conte, it is small but yummy.
I was interested to read about some of the methods the goldsmiths
used. I had assumed that the pre-columbian gold was always very high
carat, but the on the pieces in the exhibit said the gold
was an alloy of gold and copper sometimes as high as 50% by weight
(copper to gold). The explanation for the high carat appearance of
the pieces was that they were depletion gilded to raise a fine gold
surface on the piece.
I was a happy camper until I read that they first heated the piece to
form copper oxide which was then hammered off. It was speculated that
then a slurry of plant juices were applied over time to dissolve the
rest of the crust on the pieces. A detailed explanation of this can
be found by googling Sitio Conte Gold Copper Alloy or using this:.
I was a little skeptical of the hammering part of the process as it
was explained, since if I hammered a black piece of 14K in the
studio, I’m pretty sure I would wind up with a black piece of 14K
until I pickled it. Since most of the pieces were reposse’, I
wondered if they wouldn’t have required annealing during the work,
creating more copper oxide. If so, it couldn’t be hammered off
again, or could it? It also didn’t explain the wonderful fine gold
color of the castings, which perhaps could have been a much higher
gold alloy.I thought it would be fun to know from the experts here
about the possibility of hammering off the oxide, and if low carat
gold could be depletion gilded as well as these pieces seemed to be.
If so, it might create some interesting possibilities in the studio.