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Raku clay for sculpting


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#1 Isculpt

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Posted 01 March 2013 - 03:21 PM

I recently pit fired a bisqued earthenware sculpture and was disappointed to find when the fire had died down that the sculpture had broken in 6 places. The folks at the clay store suggested I try raku clay. Is it just the addition of grog that makes the raku clay stronger, or is there more to it than that? I asked if the raku clay was easy to use for handbuilding and sculpting and was told that it is. That seems too good to be true: I mean, if it handles as well as earthenwares, why doesn't everyone just use it instead and ensure less cracking and breaking? Are there quirks and tricks to working with raku clay?

#2 justanassembler

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Posted 01 March 2013 - 04:54 PM

I recently pit fired a bisqued earthenware sculpture and was disappointed to find when the fire had died down that the sculpture had broken in 6 places. The folks at the clay store suggested I try raku clay. Is it just the addition of grog that makes the raku clay stronger, or is there more to it than that? I asked if the raku clay was easy to use for handbuilding and sculpting and was told that it is. That seems too good to be true: I mean, if it handles as well as earthenwares, why doesn't everyone just use it instead and ensure less cracking and breaking? Are there quirks and tricks to working with raku clay?


Their suggestion to use a groggier clay is common for sculpting since it shrinks less and tolerates differences in thickness better as a result... Additionally, some raku clays contain things like kyanite, which has some ability to withstand thermal shock and also serves the same purpose as grog in terms of reducing shrinkage. Their suggestion to use raku clay probably was the result of the fact that your method is pitfiring and as a result your work may see some thermal shock. Most raku clays are light colored, so if you want something dark, you might have to stick with an earthenware that has added grog.

#3 neilestrick

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Posted 01 March 2013 - 07:01 PM

Many pit fired pieces are burnished to a very smooth finish, which you can't really do with a groggy clay.

You could use terra sigilatta to darken the raku clay.
Neil Estrick
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#4 Idaho Potter

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Posted 01 March 2013 - 09:19 PM

I've used Coleman's Raku (from Clayart or Laguna--it's in the studio and I'm not) for years. I make pots and do sculpture with it. If you want dark clay, just leave it unglazed--it'll turn black during the post-firing reduction step. The only problem is that most (specifically) raku clay has a wide firing range--Coleman's is cone 06 to cone 10. Which means the finer detail or delicate parts can be easily broken at the lower temperatures. If you fire to the upper end the clay will probably be more sturdy, but then it makes it difficult to use raku glazes because they mature at 05-06. I've tried firing pieces unglazed to cone 6 and then glazing and firing with raku glaze. It's difficult to get the glazes to adhere to the higher fired clay, but that may work for you. I just make raku sculpture without a lot of frou-frou.

Shirley Potter

#5 TypicalGirl

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Posted 02 March 2013 - 02:06 AM

Paper clay.
I use it for most of my sculptures, and single-fire raku most of them.
Its also nice because you can raku porcelain paper clay!
Cathi Newlin, Angels Camp, Ca
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#6 Isculpt

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Posted 02 March 2013 - 11:43 PM

Thanks for the insights and suggestions. I appreciate the info about kyanite; I heard the guy at the clay store mention that the raku clay he suggested had something in it besides grog, but I didn't catch the word. I've never tried terra sig, but this might be the time to do so. Shirley, I forgot to take into account the firing range -- an important consideration, given that I can't bisque the work very high or it won't absorb the pit fire's greys and blacks. Cathi, as for paper clay, I usually save my small clay scraps and dry them, then add shredded paper when I reconstitute them, but its so much work to turn wet clay into paper clay that I hate to bother with it. If there is an easier way to acquire paper clay (other than buying smelly, moldy clay that is shipped to me from Florida at twice the price of local clays, I'd like to know it. Again, thanks to all of you for giving me some things to consider.

#7 Iforgot

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Posted 03 March 2013 - 02:07 PM

almost all of my work is pit fired I use a clay from laguna called "speckled buff" with white terra sigilatta i have never had a problem. between myself and the other potters i pit fire with we have 50+ years of experence and speckeled buff really stands out from every other clay. B-mix clay works well too. I have tried raku clay byt i have cracking issues.




Darrel
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#8 Isculpt

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Posted 03 March 2013 - 08:16 PM

almost all of my work is pit fired I use a clay from laguna called "speckled buff" with white terra sigilatta i have never had a problem. between myself and the other potters i pit fire with we have 50+ years of experence and speckeled buff really stands out from every other clay. B-mix clay works well too. I have tried raku clay byt i have cracking issues.




Darrel
[/quote]

Gosh, Darrel, if you and your friends have 50 years of experience among you, you could be just the person of whom I need to ask this question: When I pit fire, I am looking for lots of pattern and tone variations. Sometimes I get just dull grey all over, sometimes I get all-black pots, sometimes almost nothing. What is the "trick" to getting lots of variation? Is it reducing faster? slower? smothering it more thoroughly? I know there are many ways to pit fire, and maybe there is no one answer, but I'm darned tired of trying to understand why I can do the same thing each time, but sometimes get the variations I want and sometimes just get solid color.
Jayne




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