Hello everybody,
when I pour molten silver (I usually use 800 silver) and pour it into plaster cylinders for lost wax casting, the silver oxidizes and becomes dark in color similar to black. Conversely, when I pour the silver into the sand casting mold (delft clay) the silver after it has cooled has a light yellow color without showing all that oxide that instead occurs in the other type of casting. I can't understand why this black oxide occurs and how to do to prevent this from happening. I state that I use a melting furnace with graphite crucibles and I use borax. Thanks in advance for your help.
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