"DKat" wrote in message
...
Oops - meant to say - I would only do that as a test to try to track down
what is going on. Go to clayart (www.potters.org) and do a search for
blistering or blisters in Title and Body - many ideas are there.

Wow - almost too many ideas! Hehe!

The consensus seems to be that iron can be a problem. I don't think my clay
has iron in it, as it is grey unfired and almost white fired. BUT the glaze
that is my biggest problem is red when unfired, so I am suspecting it might
have iron in it. Possibly a sollution would be to ignore the extra power
required and leave the bottom and top (lid) holes open through the whole
firing in order to provide enough oxygen?

Marianne