Firing disaster - input please

Crawling is usually more about dust or something on the pot before glazing. I don't really have any answers, but maybe there were more odd underglazes and clays there than you thought?? I found it difficult to work out your firing schedule, also I work in centigrade. Why so complicated? In my experience holding at different stages is not necessary usually. I soak at top temp always for half an hour. I know when cooling periods of soaking are necessary for crystaline glazes, but why so complicated for these glazes?

This is the firing recommended on Mastering Cone 6 FAQ and I like it. We are not doing the crystallized glazes (where you try to grow giant crystals) but our glazes do form crystals which is what gives the glazes a feeling of depth or color. Toby's red develops it's red color with slow cooling. Floating Blue becomes opalescent. The glazes from MC6 for a satin matt rather than a glossy clear.

Again, the two kilns had the exact same glazes, clay bodies for at least a few of the pieces were clearly recognizable as 112, and there were problems with pots of experienced potters that I trust to tell me if they had used outside clay or glazes and I could recognize the clay body and glazes on most pieces in any case. I noticed that I left out one piece of information. The kiln that had the crawling had not come to temperature with an Error 1 and had to be refired. There was no error with the refire and the cones looked fine. Just the pots were a disaster.

Until the second glaze firing done at the same time and with the same materials came out perfect I had tried to convince myself that it was a glazing problem (dirty pots) but it clearly isn't. I have never seen anything like this and can't for the life of me reason out why it happened.

Any chance that the lowest kiln shelf was only a few inches away from the kiln floor in either of the kilns. I have found this to have a large effect on the firing of the kiln if there is not sufficient space below the bottom shelf (at least 6 inches).

Eddie could be right, the part fired, then refired could be the culprit. I would get the kiln checked, see that all the elements are in good working order and as someone else suggested make sure your bottom shelf is high enough. Thanks for the schedule answer, makes sense, good luck. Annemarie

OK, I'm grasping at straws here. But suppose there was some problem with kiln #5 that caused one or more elements to shut down temporarily. (Loose connection, whatever.) Then the controller is calling for heat and none is coming, so it can't hold the programmed curve. BUT, the connection jiggles back into place later, causing the controller to go to maximum output to catch up. It catches up as far as the cone melting goes, but the wares have gotten a really rapid temperature rise along the way.

I think this would give the results you saw, though I'm not sure how to test this idea. Or do you have a recording pyrometer setup? If not, maybe you can run a test load and have someone check the temps every hour.

Just a thought....

Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis

We are a crafs center at a University so I can imagine this happening. I'm actually hoping that it was a one time event due to something like this (in the years the studio has been going we haven't had this happen). I'm real uneasy about risking student's work by trying to run the ramp firing again given that the old programmed 'slow cone 6' had worked just fine until it failed on the last firing. I'm tempted at this point to just attribute that to an interrupt in the schools electrical power and to stick with what has been known to work.

In the mean time I have lots to chew on. Thank you all. Donna