This is in response to a discussion about copper being included in some mine tailings and what might possibly happen if included in a pot. I have never had access to mine tailings. But I did at one time have access to "jewelers tailings." Another source for such leftovers might be tile places where they cut slabs for counter tops, etc. Sometimes they cut something other than granite or marble. Check around. You never know what's out there! And most people are quite glad to give their "waste" to some crazy potter/artist than to have to pay to have it hauled away. This is true of woodworkers and even some farmers - if their cows or horses eat grass.
This is the only pot I have left from the few that included leftovers from my gem cutting friend. He had given me shards and dust leftover from cutting turquoise and Lapis Lazuli.
This one has Lapis Lazuli inclusions along with colored (cobalt oxide) porcelain shards from a failed firing in a cone 6 porcelain matrix. It has been under-fired about one cone. At the time I didn't want the very dramatic holes and runs I had gotten with the turquoise. And I wanted a closer blend of color between the Lapis and colored porcelain inclusions. It has a clear glaze containing just a bit of a lead frit. You should be able to make out some of the runs and partial voids left behind from the Lapis melting. It was fired on its rim, so the Lapis shards seem to run up-in defiance of gravity. Lapis has no copper component, but other stones which could be used in the same way that do contain copper are Chrysocolla, Malachite and of course Turquoise.
I have not tried this sort of thing in a reduction atmosphere, or at higher than a cone 6 firing. (There wasn't enough of the stuff for all of that.) This was the result of firing in an electric kiln and oxygen atmosphere.