raku blowup
Karen Shapiro
Hi Clayarters,
I do mostly raku firing of my sculptures and don't often have major mishaps,
but ... yesterday I was firing some pieces and blew up (to SMITHEREENS!) a
piece I had put a lot of work into and could use some input into why.
It was a second firing (kiln was still very hot) into which I put the piece.
I have done this before with no ill effects. In this case, after a few
seconds the heartbreaking sound of exploding clay reached me. The piece had
already been raku-fired once, was reglazed in parts, and had dried out
totally in the sun. Was it just too much thermal shock -- too hot in there?
It was stilted on top of a hard brick -- I'm thinking it may have been
touching the hard brick, instead of being on top of the stilt.
I learned a lesson, but would like to know exactly WHAT lesson I learned!
Thanks a lot for any input,
Karen in Sonoma
Tena Payne
Karen:
I have found that 90% of the time when I re-fire a piece that has been
glazed, I loose it. I think it's cause the glaze --which remember, is
glass-- does not have the thermal shock properties that the clay does.
In other words, the clay may expand and contract rapidly, but the glaze
won't, hence breakage. Just my theory.
Also, another tip. I always change out my shelf with each successive
firing. I have a fire brick as a main support with a piece of shelf on
top. Just remove the shelf and replace with another piece.... greatly
reduces thermal shock to the next piece you put in. In fact, since I've
been doing that I haven't lost a piece.
Hope this helps.
Tena
in Birmingham where summer is in full swing.
_________________________________________________________
Do You Yahoo!?
Get your free @yahoo.com address at http://mail.yahoo.com
S.K. Tesar
Hello. On the occasions I refire a piece , I either use a hand torch
immdiately to remove carbon deposits, begin a refiring in the raku kiln
until it has "reoxidized", then remove it and add any glazes I might want
to "improve"" a situation. I have also let the piece go back into the
electric kiln with a bisque load going to O8, then reglazed some
offending part and refired. These do not always work out, but the trapped
carbon seemed to be my breakage culprit. Based on what you have said, I
would suspect that the trapped carbon under the new glazing might have
contributed to your problem.
Sandra on Keel Mountain, AL, USA
___________________________________________________________________
You don't need to buy Internet access to use free Internet e-mail.
Get completely free e-mail from Juno at http://www.juno.com/getjuno.html
or call Juno at (800) 654-JUNO [654-5866]
Dannon Rhudy
Karen, when firing raku, remove the hot brick the previous piece was
fired on, and replace it with a cold brick. Set the piece on the cold
brick. It takes an extra minute or two (and have a SPECIFIC place to
put the hot brick) but is worth that extra bit of time. Saves many a
smithereen.
Regards,
Dannon Rhudy
pot...@koyote.com
Frank Simons
Do you usually preheat the pieces for the second raku firing in an electric
kiln on low for at least 30-40 minutes to reduce thermal shock? I have found
that this reduces the chance of a major blow-up. Even placing pieces in a
range oven for a few minutes before placing in a heated kiln seems to
help.....
Frank Simons, Penticton, B.C.