Bubbly update

Marianne, every time I think of this I keep coming back to you having your peep holes open (and I'm fairly certain that is what you have open if there are 3 of them, they are on the side and they have plugs that go in them). If you are having as long a soak as you say, and there isn't an issue of the glazes being on too thick or bad glazes to begin with then you really are left with the kiln getting cold spots from the peepholes being open. Bubbling doesn't happen when the glaze is cooling off. It happens when the glaze is melting and gases in the glaze are being released. The soak at top temperature allows for the heat to be evenly distributed and for the melt to even out (bubbles to mend). If this isn't happening, then I can only think that the cold draft from the peeps is 'freezing' the glaze before it can settle.

Sorry but I seem to now be fixated on this.

Donna

Donna

These are not peep-holes, they are airing holes and their use has been explained to me many times (regarding different glazes and their firing) by my dealer - who also refurbished and sold me that kiln. I hope that's clear.

Leaving the holes open for the whole firing was a one-time event that probably was the reason for the bubbling on many of the pieces - as the room temperature was from 17-24 C, so the air being let in was too cold.

Normally, I leave the hole at the bottom and the hole in the lid open until

650 C and then close them until the kiln has cooled to 200-250 C - at which time I may open them to let the kiln cool a little faster, as it takes hours and hours for the last 200 if I don't. From an old American potter, I learned the smart rule that nothing is ready to come out of the kiln until I can hold it with my bare hands. Patience is hard, but smart.

The long hold temperature was an experiment to see if it would help. It didn't help much, so I am back to 20-30 minutes. My teacher also uses these glazes, and I am on my way over to her in a few minutes to take a look at her firing curve, as I may be using her old one. She does not have many bubble problems any more. Will be interesting to see what her curve is. BUT - her students usually glaze with less experimentation than I do - and probably thinner as well, so her curve might only bring me closer to a sollution to my most difficult glazes (the ones with the beautifier).

I am on the way to getting a new controller that will let me also controll the cooling process. I hope and pray that that will let the glazes go from boiling to liquid without leaving bubbles/pock marks. In the mean time, I am staying away from the beautifier and trying combinations of matte glazes instead. The more glossy a glaze is, the more chance of it bubbling. So I will wait a few weeks until I can have more control.

I hope this sets your mind to rest.

I have also been thinking about why Americans can not do without cones, and I wonder if Europeans "simply" use glazes that are more geared to top temperature than to heat work in total. In any case, hubby has suggested that I add the weight of what I put into the kiln onto my kiln log - thus knowing what mass is in the kiln each time and getting an even better handle on which firings work for which glazes, etc

I'm in a stress getting stuff finished to fire so I can take it with me on Monday, so not sure when I will stop by here again..

Keep smiling :-)

Marianne

Well I never cease to be amaze on how many things I don't know. This is yet another new one to me. Donna