Things You Will Need
An advantage of using propane instead of other fuel sources is that propane burns more cleanly.
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Connect your propane torch to the access port on the furnace. Then mix a cup of water with a few squeezes of dish detergent. Take a rag and dab the water onto all of the metal fittings through which gas travels. Any bubbles mean that you have an air leak. Tighten all couplings to remove air leaks before moving on -- propane is highly flammable in a mixture with air.
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Set your mold on a flat iron pan. Put on your gloves and goggles.
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Turn on your furnace. Add copper pieces to the crucible, and put the crucible and mold on the iron pan to preheat it to at least 100 degrees Celsius and start heating the copper. Ensure that the pan is completely dry when you put it into the furnace.
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Remove the mold using the tongs when the metal starts to turn a dark red.
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Observe the copper as it heats to estimate the temperature at that point in time. Metal will start to show a dark red light at 480 degrees Celsius, becoming an orange-yellow at 1,100 degrees; at this point, you're very close to the melting point of copper.
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Remove the crucible using the tongs. Turn the crucible to pour the liquid copper into the mold. As the copper solidifies, it wil take the shape of the mold.