BronzClay firing problems

I discovered something very interesting yesterday which I think is pretty important for anyone working with bronze clay.

I had some problems with the second firing I did in the class. They all came out looking very dull, with a deep matte dark or black patina. One of the pieces broke when only a little pressure was applied.

This is the fourth batch I've fired in the new kiln, so I don't think the kiln or wrong temperature setting is the problem. Everything else was the same apart from that I added some new charcoal to the pan - I've always used charcoal straight from the packet (no pre-firing) so I don't think that is the issue either.

Having looked around at what other people have said, I think the problem is that I tried to remove the pieces from the pan whilst they were too hot. There has been some reports that this can cause them to go brittle.

I'm still not sure if this is the cause, so I'll refire the remaining pieces to see if it makes any difference.

I'll also put in a few sample scraps, so I can take one out whilst really hot and compare the strength against another which I'll let cool off slowly.

I'm really upset as these were students pieces, so am keeping my fingers crossed that the re-firing will do the trick. I guess this is what happens when you work with new materials - but being a teacher it is extremely upsetting when you mess up a students work.

I'll let you know what happens, and will post some pictures later this week.