10K Gold Acid Test Discrepancy: Understanding the Results

Question
Hello, when I test some 10k items with acid and a stone the line will disapper after a little while but when the acid is placed directly on the item it does not turn green or bubble at all.  This is on some 10k items not by any way all of them I test.  Do you know the reason behind this and should I just check all items directly on the piece. Just wondering why the difference between the scratch test and putting the acid directly on the piece.  
Thanks, Jim

Answer
Hello Jim and thank you for your inquiry. Sometimes on heavily gold plated items it will show up as lower karat gold i.e. 10kt. If there is a place where you could test on the item, I would go that route. Sometimes just not enough of the gold comes off on the stone with lower karat gold to tell the difference in heavy plate and gold. Be very careful though when testing on the item and remove the acide quickly. Hope this helps.

Sally
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