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I am new to jewelry. I would like to try casting silver (pure) in so called green sand. In my research I see that it is recommended to use some sort of flux while melting silver. The most popular and widely available without a doubt is borax (sodium tetraborate if I am not mistaken), however it seems to be for some reason (toxicity maybe) illegal where I live and I cannot get it that easily.

Are there any common materials that can be used as flux for silver melting instead of borax?

I have seen sodium carbonate (wash soda/calcined soda) being sold as some sort of flux and I have read something about sodium hydroxide (lye) being used as flux in some applications. Would these materials be suitable/better than nothing for silver melting or should I not worry about it at all and pure(ish) silver should not oxidize anyway? Or is there anything else that might work?

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I would suggest charcoal and no flux. Keep molten time to a minimum. Charcoal is used on molten lead for long periods to reduce oxidation. For many copper alloys , hydrogen absorption is a problem ; it evolves during freezing causing porosity. I read in ASM Metals Handbook that molten silver may absorbs oxygen causing porosity. Charcoal should provide some protection from both H and O.. Borax seems pretty easy to get in the US. However, long ago I mixed flux to make a slag for copper alloys , it primarily contained : soda ash ( sodium carbonate), beach sand ( silica), and fluorspar. There are a number of sites on the net that sell proprietary fluxes ( for copper alloys). And one site gives info on the flux components - 911 metallurgist.

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  • Could you please expand on the possible method of usage a bit? Would I just sprinkle it on? Wouldn't it just burn? It ignites in air at around 350°C, and we are talking about over 1500°C.
    – Martynas Žiemys
    Apr 7 '20 at 18:04
  • First get a new reference; silver melts at 960.8 C. Any of the typical alloys like Cu will lower the melting temperate. For casting 50 C should be enough super-heat. Even less with a hot investment mold, The charcoal will slowly burn generating a CO + CO2 atmosphere . I remember about a 1 to 2 inch deep charcoal bed. Charcoal granule size of roughly 1/4 ". No fans blowing at the crucible.
    – blacksmith37
    Apr 7 '20 at 18:38
  • I know what temperature silver melts at, however if I understand it correctly it must be higher in order to flow to the mould successfully and the temperature of the torch I am planning to use is advertised to be 1900°C(so I expect it to be at least something above 1500°C). Should I lower the temperature by adjusting how much air gets to the flame? Have you tried it yourself? Don't get me wrong - I really appreciate the advice and will give it a go, I am just curious what to expect.
    – Martynas Žiemys
    Apr 7 '20 at 19:04
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    The 50 C super-heat should handle it unless you are trying to cast thin section like 1 mm /0.040".My only experience was commercial except watching a dental lab pour Vitallium ( Co + Cr) and they used no flux for fast induction melting.
    – blacksmith37
    Apr 7 '20 at 19:22

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