I've done a test at my school on a small piece of the bi-metal,
but the solution ate through the asphaltum in 30 minutes and didn't
etch the gold at all. It's possible that the school's acids aren't
quite right, so I'm planning to purchase my own.
Aqua regia is an extremely aggressive acid mixture it will attack
many resists I am not sure of any type that will stand up to long
exposure in it. I did find on the web some references to using a
mixture of beeswax asphaltum as a resist for aqua regia so you might
try to mix the asphaltum with beeswax. The second problem you have
is that the silver in the 22k alloy it will form a film of silver
chloride which will act as a resist and stop the etching of the
gold. This is probably why you did not see much etching of the gold.
One way to deal with this is to alternate between the aqua regia and
a solution of aqua ammonia which will dissolve the silver chloride.
It will be a slow process.
James Binnion Metal Arts
Phone (360) 756-6550
Toll Free (877) 408 7287
Fax (360) 756-2160
Member of the Better Business Bureau