Bloating blues

I managed to get the kiln up and running again this week..the bottom element had burned right through and needed replacing. The first stoneware firing with the new element wasn't a great success as the red, stoneware clay I'd used on some of the pots bloated very badly. I guess I was taking a risk as it's rated to 1250 C and I took it to cone 7, pretty much on the limit. Most stoneware clays you can push a bit further, but not this one it seems, so next time I'll have to use a lower firing transparent glaze.

I like the effect of the white slip over dark clay..the big problem is finding a stoneware clay which will turn dark enough without a reduced atmosphere.

Sake cup with Kohiki glaze. Bloating mainly on the inside wall

The guinomi below has just the depth of surface I'm looking for. It was made from re-cycled stoneware clay and fired in reduction first time around, in a saggar, then re-oxidised in this firing. Surprising how much shinier the glaze is on this piece, perhaps because it was fired twice.

Guinomi with Kohiki glaze

I also tried out a new glaze made with cornish stone as the main ingredient:

Cups. Left  was oxidation fired, right heavily reduced

I think the glaze needs to go alot higher, perhaps cone 9 or 10 to get a full melt of the wood ash in there. Cornish stone can give similar results to potash feldspar but contains more silica and less of the fluxing oxides, which is why I included a fairly high proportion of washed ash (18%) in the glaze. Well, all this may be fairly irrelevant, as I read on the Potclays website that they stopped mining this stuff in 2008! They do make a synthetic substitute, but it looks expensive, and whether it fires the same is another question..