One of the techniques that I was taught for “cleaning” contaminated
gold or silver was to add a pinch or two of Potassium Nitrate to the
crucible while the metal was molten. This results in the formation of
a black “clinker-like” crust, which is then removed with a graphite
rod. The remaining metal is then poured into an ingot mold. The Black
cindery crust or scab is then left in Hydrochloric acid until it
dissolves and any remaining original metal (silver or gold) can be
recovered from the acid as small pieces. It may sound like a “bush
remedy” but it works. My question to the knowledgeable orchidian
community concerns the chemical process that takes place. Has anybody
done the same? What is happening when the KNO3 flashes and the black
crust forms? I have searched the web to no avail. I would appreciate
any light shed on this as I do like to know what I am doing from time
to time.
Also would like to take the opportunity to wish all Orchid members
the very best for 2009.
John Bowling