wich metal will not dissolve in STRONG ap?

[lanfear]

Hi guys. I have tried to search the forum, and also tried to implement the solubility chart. But could not find an answer. The case is I found an old tie clip. It has the markings 835 and 21.
These markings are obscure and don't tell me anything. It has a golden layer on top and a silvery core.
So i thought maybe it was gold filled. My only way of testing is stannous. So I cut off a small piece and put it in 50/50 HCl30%/H2O2 35%. But i got no reaction at all. Only allot of bubbles from the oxidizer.
Anyone have a clue to what material could be withstanding this strong solution?

 

[Lou]

Might be titanium nitride. Has golden sheen and isn't well soluble.

Silver doesn't dissolve too well in AP either and breaks down peroxide catalytically.

 

[Lino1406]

1. Seems silver 835 + gold 21
2. As Lou said, both catalyze peroxide decomposition
3. What you want to do next?

 

[lanfear]

Would not some of the Au go into solution if it was present? Need to test with stannous when i get home. I'm pretty sure that there is silver in this clip. Because I tried with a drop of HCl on it. And it smelled like AgS. At this time I neither have the resources nor the experience to handle this kind of material. I was just curious and wanted to experiment with some of the processes that I do have some grasp of.

 

[butcher]

if it is silver with gold plate, scratching the piece on a test stone, drops of nitric will dissolve away the silver and base metal, leaving the gold streak, this test can also be compared to scratches of known gold content next to the scratch of the piece being tested, nitric acid or various concentrations of aqua regia to attack the scratches will let you determine karat of gold.

Filing a notch through the plating scwhertser's solution, (silver testing solution) (potassium dichromate dissolved in dilute HNO3), will test for silver and base metals, pure silver giving a red color and .800 silver more of a brown red color (copper gives brown in solution).

Hokes also wrote a book on testing precious metals ,there Is a link to it on the forum, sorry I cannot point you to it, But I bet it can be found in the book section or with the search, Pawn broker Bob (a forum member) Has a great little book on testing of precious metal to find his book I would search his name an posts.

 

[jeneje]

Another test for silver, take a test stone, take the piece and rub it on the stone several times. Take the 18K testing solution and put a drop on the scratch, if it turns a pale blue it is silver. Make sure the testing solution is 18K.

Ken

 

[lanfear]

thanks for the good solutions. I don't have access to nitric at this time. That is my problem. But I will try to get a testing kit off fleebay or amazon. I will need one in any case.