At first glance I thought all the test pieces we fired in the pit fire were black, just black. But look at this pinch bowl, after washing there is some gold and blue. This bowl is red stoneware with Florida clay slip applied around the perimeter and bisque fired beforehand. We used citrus fertilizer, miracle grow, and salt sprinkled liberally over the wares before firing, nothing else.
Keep in mind the pieces we fired are test pieces. This one is what I call a brush holder, open at the top and bottom. This was fired green, no bisque. Amazingly it did not crack or break. Food for thought.
This pinch vase was bisque fired beforehand and got smokey color and one tiny spot of copper color. Why? I have no idea. We placed pieces of copper inside the pieces, but I think the copper was too thick to melt and produce the color we were looking for.
This flower form was bisque fired beforehand and only has carbon colors showing.