I used to melt (copper) buss bar that came from silver contacts. The copper was cast in ingots for use in recovering silver from nitrate solutions. The buss was often silver plated, so using it as I did resulted in recovering the small amount of silver that was included in the plating and any of the remaining silver solder.
If you have a crucible furnace, it's easy enough to melt copper, but keep in mind it melts just under 2,000°F, so it's a bright yellow heat when up to melting temp. I used an ingot mold for my copper, coating it well with lamp black to avoid soldering the copper to the mold, which was made of cast iron. Get the copper molten, then pour when it's above the melting point by 50° or so, enough to made a decent ingot without cold flows. A graphite clay, or silicon carbide crucible is acceptable. Do not use flux. You may have to skim the copper before pouring, but flux will cause the metal to fuse to the mold under bad conditions, and it's not easy to remove from the ingot. It's not really necessary if you're melting clean copper.
Be certain to preheat the mold to at least higher than the boiling point of water. Don't get it so hot it starts burning off the blackening, which is a must, to insure you don't get fusion with the mold.
A room temperature mold has the potential to flash to steam, the miniscule amount moisture that is contained on the surface. It can be the source of a dangerous eruption of molten metal, regardless of it being silver, copper or gold.
If you have considerable trouble with your metal including gasses, you may have a degree of success covering the surface with charcoal, which will consume free oxygen.
If you can handle your ingots immediately (use tongs), dump the mold the moment the copper solidifies and plunge the ingot into a large container of water. That will cause the oxides to shed, leaving behind a clean surface. It will have considerable scale if you do not.
Hope some of this helps. It worked for me! :wink:
Harold