Raku Breakage - help!
Posted 11 September 2012 - 12:53 AM
My last firing was a bust. I had a pot so large it gave us about 2" on either side of the kiln. I used Continental Clay Raku glaze and some of the Spectrum series (I've had great luck and amazing metallics with the latter). The inside bottom of the pot did not mature and the glaze bubbled. I assumed it was the size of the piece.
So, from 1650F, I allowed the kiln to cool to 800F, hoping that this would ensure that the relief I had made would take the shock. Both were made from a raku clay body. As soon as I placed it in the kiln, it partially broke. I removed it and quickly attempted to mend it as a last effort with no success. Then, as the temp increased, it broke in half. I've not revisited my raku kiln since, because of the risk. I have an art show in under two weeks.
How can I ensure the ware is warm enough to place inside the kiln? Simply by setting it on top? I think that 800F was far lower than I should have had to reduce the temp to. Can someone help? I cannot attach photos at this time. :-/
Posted 11 September 2012 - 09:10 AM
What was your clay body? What is its cone range and what temp was it bisque fired to? How long before firing did you apply the glaze? With that large pot, I would have applied it the night before to make sure it and the pot were dry.
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Posted 11 September 2012 - 01:29 PM
Posted 11 September 2012 - 06:42 PM
I found I got great color in the environment. For your relief, I am not sure how thick and thin the various thicknesses may be. That could be your cracking problem. For something like that, put it in the first batch and fired a little slower. I don't think leaving it in the kiln to 800is a good idea because you miss the good reduction temperature. Are you talking 800 F.? You have also passed through Quartz inversion.
MacDoodle mentions a good point. placing pieces on bricks. I use bits of fiber too sometimes or coils just to get the piece up off the shelf and to have the heat circulate. I think you could have used that for the large piece that had a bubbled glaze on the inside. If the bottom was flush with the shelf, it may not have gotten hot enough on the bottom.
From AIR Vallauris, France
Posted 12 September 2012 - 07:47 AM
Posted 12 September 2012 - 10:26 AM
The studio I was working out of recently closed, so I have been recently forced to pay-per-pound at a completely different studio until I can close on my house and my kiln arrives. I was a bit rushed to continually produce, as I have a 6-day show in less than two weeks. I don't NEED Raku pieces for it, but I do have some very beautiful metallic pieces and wanted to expand my collection. Since that incident, however, I've not returned for fear of breakage. I am a hand-builder (slab pots and sculptural pieces), so it can take me a while for one piece. Anyway, to answer the question, she bisque-fires at 06. I have had problems, however, with glaze coloring, warping of my clay, and pooling of glaze (none of which I have had before), so it has been a bit frustrating. Can't wait until my kiln arrives!!!
I really appreciate all of the help!!! Now that it is cooling even further in Wisconsin, I will certainly be better prepared.
Posted 12 September 2012 - 11:09 AM
glazing big stuff the day before is also a good call
laguna WSO stoneware is a superb, reliable clay for all sizes of raku...dry big stuff slowly, like, weeks...bisque slowly, cool bisque slowly...patience is a big factor in raku even though it happens fast
Posted 12 September 2012 - 03:54 PM
The cracking is not at all related to the pot being wet from the glazing. It would blow up if that were the problem, not just cracking in half.
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