Alaa,
I don't think there's any test using powders for gold purity without destroying one of your coins (cupellation).
I think you need a different goldsmith. Find a goldsmith with an acid test. If you want to know what it is, then search google for "gold acid test."
There are also electronic testers, but your best bet is an acid test.
I'm sure everyone is anxious to see those fine resolution images!
Obv. ALOY MOCENI – S M VENETV / DVXSt. Mark and Doge.Christ in Mandorla.
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