How to remove gemstones from slag

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learningnewthings

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Dec 4, 2021
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Hi everyone, I am currently melting gold scrap into bars and to do so I add in borax as flux. After the melt I am left with hard borax slag. Is there a way to recover gemstones stuck in this slag? I am struggling since the slag is not only borax but also other impurities.

If you have any questions let me know.
 

Elemental

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Sep 17, 2020
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Charlottesville, VA
It sounds like you are taking different karat gold jewelry and just melting it together into a bar. Is this the case? The borax as a flux is not going to remove the various metals used to alloy the gold. I always remove all gemstones, bits of cardboard filler, epoxy, tiny iron springs found in clasps (I hate those things, but a strong magnet will catch them) before processing. I also hit the material with a propane torch to incinerate/remove anything else. It's painfully time consuming, but helps before I inquart with silver and cornflake to then chemically refine.

I suppose the question I have for you is what is your end-state? Are you planning on chemically refining, selling your bars as is, or just holding the gold. By mixing all the different karat gold together, you may have a harder time selling it, it will also make it a little bit more complex to process. Are you testing your scrap jewelry before melting? A couple pieces of fake costume jewelry will really contaminate you gold bar with various metals.
 

learningnewthings

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Dec 4, 2021
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It sounds like you are taking different karat gold jewelry and just melting it together into a bar. Is this the case? The borax as a flux is not going to remove the various metals used to alloy the gold. I always remove all gemstones, bits of cardboard filler, epoxy, tiny iron springs found in clasps (I hate those things, but a strong magnet will catch them) before processing. I also hit the material with a propane torch to incinerate/remove anything else. It's painfully time consuming, but helps before I inquart with silver and cornflake to then chemically refine.

I suppose the question I have for you is what is your end-state? Are you planning on chemically refining, selling your bars as is, or just holding the gold. By mixing all the different karat gold together, you may have a harder time selling it, it will also make it a little bit more complex to process. Are you testing your scrap jewelry before melting? A couple pieces of fake costume jewelry will really contaminate you gold bar with various metals.
Im just holding the gold for now, is there a way to remove the gemstones from the slag in hindsight?
 

Elemental

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Sep 17, 2020
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Charlottesville, VA
I would recommend using ethylene glycol (found in vehicle anti-freeze), as it will dissolve the borax but shouldn't hurt the gemstones. Acetone will also work, but much more slowly. There are acids you could use as well, but you'll likely damage the gemstones, assuming they were not already damaged by heating to gold's melting temperature.

I do not have experience with this procedure (just going off of a chemistry background and a bit of Google-fu), and it may be worth it to melt some borax with a torch and then see how it dissolves in ethylene glycol first. You may need to heat the solution to speed up dissolving. Good Luck
 

voidforged

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May 10, 2020
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Nevada
The stones more than likely cracked or shattered during the melting process, and also probably partially or completely dissolved into the slag depending on the stone type.
 

nickvc

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birmingham
Unless you are melting large volumes I’d suggest removing the stones manually , once melted you can dissolve the borax with hot water as Lino suggested or crush the slag and again manually sort the stones out , chances are many will be already damaged so either route will make little differenc.
 

orvi

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Apr 13, 2021
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applying heat to finely faceted stones is not a good idea, they could often crack or develop defects. as mentioned above, when using slag, it help oxides, inorganic impurities and similar stuff dissolve and clean the resulting metal.
but stones mainly fall in this category, meaning, they will likely combine with the slag (if the temperature is high enough)... any type of faceted quartz (ametyst, citrine etc...) will do so, and many more like garnets, zirconia or topaz will likely do the same. at least, the fine polished facets will be likely ruined, as borax will at least "etch" them on the surface. not mentioning diamonds will likely burn away :D
 

upcyclist

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Sep 28, 2015
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Maryland, USA
If you're just holding on to your gold, I strongly suggest not melting into bars--it needs to be in smaller pieces to refine anyway. If you're going to attempt chemical refining in the future*, don't even melt it, because you'll be melting it as part of that process when you inquart (alloy) it. If you must melt it for size reasons, cornflake it (melt into small flakes by pouring into ice water from your crucible). The cornflakes will easily melt, and are easy to portion out.

I wouldn't worry about recovering gems from the slag--once you've gotten them hot enough to melt a gold alloy (much less a brass alloy for the plated stuff), you've likely destroyed anything that's not flawless. The best solution is to pull them (as others have suggested) before they even get to the crucible.

Some folks also process karat gold by putting it straight to aqua regia, because the stones end up on the bottom, and if they're still clear, they're diamonds. If they're hazed, they were Cubic Zirconia anyway.

*and if you're not considering learning any kind of refining, save your self some time and throw it in a baggie or bucket, and find a refiner that will remove & return any stones. Even then, the stones are only worthwhile if you can identify and sell them. About the only stone you'll be able to sell easily as a commodity will be diamonds.
 
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