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Casting .99% Copper

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You're right Thomas, I did miss read it, thanks for setting me straight. Your donig better than the back doctor has been able to do :D I still think I'll try my scrap pewter and see how that works since it's mostly tin :blink:

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Last summer I was casting bronze at the local Thresheree. We used an alloy of about 88% copper and 12% tin by weight, a classical bronze alloy.
Small A-1 graphite crucibles were used and we melted approximately 1-1/2 lb. batches. I had used a small amount of aluminum melting flux 'cause thats what we had.
It cast well and all the castings were poured in petrabond sand. We also discovered that the initial melt, ie chunks of tin and chunks of copper melted in about 80% of the time that it took to melt chunks of bronze of an equal total weight. We figgered that the tin melting first provided a hot pool of metal to conduct the heat into the copper faster.
We did not do brass last year as I did not have a pyrometer at the time. Overheat brass and nasty zinc oxide is formed... galvanizing poisoning... to be avoided.
The bronze did not seem to be as susceptible as copper to oxidation, but that is only an impression... no science content.
Another source of tin is 95-5 tin lead solder.

paul

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Thanks courtiron! Thats very helpfull. I'm just starting to read up on flux and what works best for what.

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The old boy that taught me much of my casting said that in the old days they used broken up beer bottles as a flux for bronze. Gunmetal was an alloy of about 2% lead and 8% tin, now instead of lead I think they use zinc but having poured the older version it too pours real easy with the additions of a little lead. When we talk of having trouble pouring copper and the ancients didn't, we are pouring 99.9% pure and they were not. They were pouring an alloy of silver, lead, tin or just about any other non-ferrous metal that was in the parent ore. This mishmash of metals are sometimes pretty easy to pour and a lot tougher than one thinks. There was a program on Nova this week on the Great Sphinx and how it was built. They showed this sculptor in the USA using stone and copper tools to make a nose. The copper tools were made of pure cooper rod, this I don't think would have applied to that period. Their tools would have been of the native copper type that had a mix of non-ferrous metals in them such as I have already mentioned, much tougher than 99.9% copper for tools.

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bentiron-
I've heard about people using glass as a flux before but never with bronze. Would you suggest I use it with the mentioned tin/copper ratio? I'm assuming I would put in enough glass to form a thin plug over the top of the moltent metal....

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Would I suggest it? No, not necessarily so, it is just something that my old mentor mentioned using in the deep dark reaches of his past. When I was doing experimental traditional bronze casting for that archaeologist I just use borax as a flux and it worked fine as a flux on top of the melt.

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