Steve, though I don’t understand the exact nature of your problem
with the firescale on your gold, let me suggest that you could try
Make up a solution of the sodium bisulfate, add some hydrogen
peroxide (H202 – should be available in a drug store [or at the
chemist’s, if you’re a Brit]), heat GENTLY, add the gold piece. You
may eventually begin to see tiny bubbles rising from the piece,
showing that the firescale is being chemically removed. If not, add
a little more of the sodium bisulfate and/or hydrogen peroxide.
This is a slower process than trying dilute (50:50) nitric acid, my
personal favorite for firescale. But the ingredients are a lot
easier to come by. HTH (Hope This Helps).