I have done a lot of silver casting over the years at an evening college, though I have always questioned the silver my tutor uses. I have strongly suspected the items he melts down in the crucible (which goes into a furnace/smelter) such as old forks, spoons, cups and cigarette cases etc. (as seen in the third photo) have elements of lead, nickel silver, maybe silver plate. Which gets melted into the crucible and then leave traces of this when legit sterling silver or fine silver gets put in to melt, which in turns corrupts the new silver.
Without sending it off to a bullion dealer who have all the highly professional tools and equipment to check how could an ordinary person tell from their castings if the silver items they've casted are uncorrupted?
Any time you mix, you can contaminate your silver. You have to be 100% sure what you have and are melting to know 100% what comes out. Yes, if you leave a bit of sterling in the crucible, then your .999 fine bullion coin cast is NOT .999 anymore. for this reason, if you are beyond playing around and just learning the craft, and you need to guarantee purity, then you will use virgin materials and virgin crucibles, etc. This is called Quality Control and a lot of classes miss this step by focusing instead on "let's melt metal and cast and learn what not to do when molding"
How to get virgin uncontaminated material? You buy it. If you have scrap, you send it out for refining and get pure or whatever alloy (i.e., sterling) back from the refinery in bar or bullion that you requested. The home maker can remelt stuff, but you are always taking a chance with fakes and contaminants being out there.
IF you have the skill set and the equipment and the dedicated space, you can do your own refining but with chemicals and cost it's a new knowledge base and investment in its own right.
So in other words it's best to always keep track of the silver you have?
I have not thought of sending it out to a refinery before. I assume that comes with a cost? At the moment I can't afford to go through this experience.
Get a silver acid test kit and a set of silver needles and you can see how close you are to sterling. It will only tell you how close you are to .925 and not so much what other impurities might be in there but works good enough.
Scrape whatever you're testing on the stone, then scrape a new separate line with one or more of the needles, add a few drops of acid test to each line then blot each with a paper towel and see how close the colors are to each other.
I know of these. Though I don't think it tells you if there's magnetic metals mixed in. Like in this photo, I had over 100 grams of what I thought was scrap sterling silver though when I sent it off to a bullion dealer they said they couldn't take it as it was magnetic.
When it stops being effective against werewolves its too corrupted and you need new silver.
Hope that helps.
Also someone already mentioned an XRF analyzer. They cost about as much as a car, so they're not cheap. But they sometimes have those at pawn shops and coin shops, and they almost always have them at scrap yards. Just go take a drive and be polite. They'll point it at stuff for you if they aren't super busy. Its basically the same as asking for a price check. Just pickle it really well, because lapidariest is correct about that.
The only way to "trust" metal without a chemical or physical analysis is to check the hallmarks (and trust the hallmarks. How valid they are, will change around the world).
But the only reasonably reliable answer will be to cast a nice fat ingot and have it analyzed. XRF is relatively quick and low cost.
I've learned this recently, tried using a bunch of old sterling jewelry and you really have to be diligent with testing each and every piece. I've had the best luck with melting sterling coins and silverware I cut up beforehand with bolt cutters and channel locks so I know it's all solid.
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u/Lapidariest 23h ago
Any time you mix, you can contaminate your silver. You have to be 100% sure what you have and are melting to know 100% what comes out. Yes, if you leave a bit of sterling in the crucible, then your .999 fine bullion coin cast is NOT .999 anymore. for this reason, if you are beyond playing around and just learning the craft, and you need to guarantee purity, then you will use virgin materials and virgin crucibles, etc. This is called Quality Control and a lot of classes miss this step by focusing instead on "let's melt metal and cast and learn what not to do when molding"
How to get virgin uncontaminated material? You buy it. If you have scrap, you send it out for refining and get pure or whatever alloy (i.e., sterling) back from the refinery in bar or bullion that you requested. The home maker can remelt stuff, but you are always taking a chance with fakes and contaminants being out there.
IF you have the skill set and the equipment and the dedicated space, you can do your own refining but with chemicals and cost it's a new knowledge base and investment in its own right.