What is the old adage, "you get what you pay for"? Though I am fully aware of what happens when you over-saturate a glaze with oxides (carbonates, etc.) my recent tests with manganese dioxide were exceptionally promising right up through small cups as tests. I made up enough to dip several pots, a teabowl and a small covered jar and fired them in my most recent firing and you know what happened, crap happened. The surfaces just boiled and droozed creating something resembling over burnt metal. Just nasty to say the least. When I opened the kiln, the only thing I can remember is saying; "CRAP", later it became very apparent that I was very lucky I only fired the two pieces and on tiles that were on top of bricks or I would have had a real mess. Like something out of the ALIEN movies, the glaze dripped off the pots and burrowed their way through the soft brick tiles and stopped at the hard brick underneath. Sorry for another oft used cliché but in this case, chance does favor the prepared mind at least in terms of when crap indeed happens.