In the Cava Lab cooking up new materials at 1400 degrees Celsius can really get materials stuck to the containers. We try all sorts of things to clean the alumina (Al2O3) containers. In this method, we attempt to dissolve the contaminants in a molten glass, which is then poured out of the crucible at 800 degrees Celsius onto an aluminum plate where it beads up and cools. That lovely blue came from some crusty black cobalt oxide that was a little too cooked.