QuestionHello Tom I use 18k acid to test silver it turns bright white for .925 a duller white for lower grades have you ever heard of this? Also I find not all 18k acid will work is there a difference between 18k with a white cap and 18k with a red cap? the acid with the red cap will work the white cap will not.I have problems seeing the different colors with the silver testing acid on the black stone can you help.TKS Dave
AnswerHello, Dave.
Actually, I have not normally used 18k acids to test silver. As I recall, when doing that on a testing stone the mark generally is dissolved away to quickly to make any determination. I have put the acids generally used for gold testing directly on suspected items to see if any green bubbling happened telling me the item was copper based of some sort and not silver through and through.
Directly on silver the acids would give me a grayish white for sterling and a darker grayish color for coin silver and below. I have found specific acids and additives used to test for silver do a much better job than the nitric acids and the stronger nitric/hydrochloric mix used for high karats. (Hydrochloric alone is not very useful for metals testing of gold or silver.)
As for the acids from your two bottles reacting acting differently, there is not a standardized bottle cap color of which I am aware. We have purchased the acids from more than one supplier and while some might have the same color bottle caps others do not. You cannot go by the bottle cap color. Who knows why one works and one does not. Acids can absorb water and loose strength over time if not perfectly sealed. Metal test acids have a reasonable shelf life but depending on storage can weaken sooner than one might think, still usable when the test uses a comparison with a know sample providing the acid is strong enough in the first place.
With a test stone or even is putting a drop directly on the metal, the best results come from a comparison with a "known" sample. For instance, use a piece of metal which you know is sterling (or gold or what you are testing for) and use both it and the unknown one for the rubbing streak on the stone. If applying directly, do the test to both the known and the unknown. If the unknown matches the results of the metal you are already certain about, then you can figure the unknown is the same metal. If not, then it is not.
Yes, a thin rubbing on a slate test stone is hard to see sometimes. That is certainly more of a problem if the acid dissolves the streak away quickly. You need a reaction but slow enough to see the actual results and comparison with a known sample. As long as you compare with a known sample, the designation of the acid as 14k or 18k, etc., is not so important as the comparisons of the samples. Yes, the acid must be strong enough to react with the metal and not so strong as to react too quickly to get a read of the reactions.
Dave, thanks for the question. Feel free to use a follow-up to get back with me if need be. Oh, and if you get a chance please take a moment to rate the answer so I will know how things are being received on the questioner's end. Fair enough?
God Bless and Peace. Thomas.
