I can't believe I did this. I fire in an electric kiln. I was rushing to get in a ^6 GLAZE firing for an upcoming event and I use an 04 cone in my kiln sitter instead of cone 6. In the morning I'm going to take all the cones out and restart it but now I don't know if I should try to fire it to ^6 or try firing a cone lower since it has already gotten some heatwork. I'm afraid all the pieces will be overfired if I fire to ^6 now. Anyone have any experience with this one? Thanks, Crystal
No experience with this as such, but I'll be glad to throw out my
2 cent's worth on "heat work". I see this as a lot like conventional melting, such as ice to water. Ice nominally melts at 32F (0C). Now let's say you have a large block of ice you want to melt. If you take it to 33F for an hour, you only get a little bit of it melted. If you want to melt the whole thing and never go above 33F, it might take many, many hours. Or you could take it to (say) 60F and it would melt much faster.
But you can hold it at 31F forever and it won't melt.
So my point is that "heat work" has to be considered relative to the melting point of the material. In the case of ^6 glazes, the ^04 firing doesn't get very close to the melting point, so it contributes negligible heat work.
Now clay and glazes are not exactly like pure water, since they are mixtures of many substances with different melting points, plus there are eutectic effects that can lower the overall melting point below any of the individual ones. So, yes, there probably is a small amount of melting that happened in your ^04 firing, and if you held the kiln at the peak ^04 temperature long enough you would probably have a noticeable effect. But I'd guess this is probably not going to be a problem in your rcase.
Best regards,
Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis
Thank you both so much. I feel a lot better now. In the 8 or so years I've been firing the kiln this has never happened so I had no idea how the next firing would react. Guess I've been pretty lucky. I'm re-firing right now. Whew!
I had a similar experience once. The center ring of the kiln didn't fire and I wasn't aware of it until it was too late. It happened on the bisque load, prior the glaze load too. Didn't notice it on either load.....(don't ask why - the head just does that sometimes). I refired the glaze load to Cone ^6 and all but two pieces came out fine. The two had bubbles. I believe the bubbles were caused by the bisque being underfired and possible bubbles at that point. They just didn't show up until the high fire.
I have also "refired" Cone^6, more than once. It works out fine. I have a friend that will refire up to 6 times. I have only done it twice. Can't afford the electric bill!!
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