Clay for smoked/pit fired pottery that has not been bisqued
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Clay for smoked/pit fired pottery that has not been bisqued CNB 08-26-2006
Posted by CNB on August 26, 2006, 2:05 pm
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Hi,

I make smoke fired pottery and have always bisque them at a low bisque
temperature but I'm looking for alternatives for people that I know do not
own a kiln. I'm planning on doing some smoke-fired burnished pottery pieces
and I'm wondering what I should start to look for in a clay if I am NOT
going to pre-bisque the pieces. Should I look for a clay that contains grog,
sand or a combination? If so what should the mesh size be and what
percentage should be in the clay? Should it be earthenware or stoneware or
does that matter? Would my best bet be for a raku clay? If someone out there
only knows the name brand of the clay I could probably look the information
up but I only have a couple brands available in my area. I know I could
contact them but I would prefer information from people that know about it
first hand.

I know that I have to worry about thermal shock and pieces breaking but I do
have some ideas on how to remedy that if it does happen. This will be an
experimentation in itself, but my thinking is if I start with the best clay
for this type of work the breakage should be reduced. Any and all
information would be greatly appreciated. Feel free to reply to me directly.

Thanks,
Crystal





Posted by Steve Mills on August 26, 2006, 7:45 pm
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I have always recommended that people in your situation or a similar
one, use a really coarse Stoneware/Raku clay, BUT overlay it with a slip
made out of the SAME clay minus the grog.

That way you have a body that can handle thermal shock, but at the same
time have a surface that you can burnish to a high gloss if you wish to.

The same technique can be used if a clay with a high colour is needed,
for example a blue or black.

To put loads of expensive oxides in a body when only the surface 3
percent is visible at any one time seems to me to be fairly pointless,
quite apart from the effect of a lot of fluxing oxide has on the whole
piece!

A good coat of slip can work wonders and open many technique options.

Steve
Bath
UK



>Hi,
>
>I make smoke fired pottery and have always bisque them at a low bisque
>temperature but I'm looking for alternatives for people that I know do not
>own a kiln. I'm planning on doing some smoke-fired burnished pottery pieces
>and I'm wondering what I should start to look for in a clay if I am NOT
>going to pre-bisque the pieces. Should I look for a clay that contains grog,
>sand or a combination? If so what should the mesh size be and what
>percentage should be in the clay? Should it be earthenware or stoneware or
>does that matter? Would my best bet be for a raku clay? If someone out there
>only knows the name brand of the clay I could probably look the information
>up but I only have a couple brands available in my area. I know I could
>contact them but I would prefer information from people that know about it
>first hand.
>
>I know that I have to worry about thermal shock and pieces breaking but I do
>have some ideas on how to remedy that if it does happen. This will be an
>experimentation in itself, but my thinking is if I start with the best clay
>for this type of work the breakage should be reduced. Any and all
>information would be greatly appreciated. Feel free to reply to me directly.
>
>Thanks,
>Crystal
>
>
>
>

--
Steve Mills
Bath
UK

Posted by CNB on August 29, 2006, 9:32 am
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Hi Steve,
Thanks for your reply. I figured I'd have to use the slip. Guess I was
hoping for some magic bullet. The one I'm using doesn't really need the slip
but I also bisque it first. That is true that we will have more options of
decoration. I'll just have to find the time to make the slip before we have
our get together. We would have more fun with it though.

Can you define "course" for me? As in, what percentage and mesh sizes of
grog/sand/kyanite that would make a"course" clay? I'm looking at two
different suppliers and they're not all described like that. I don't know
what percentages and mesh sizes I should consider "course". Hate to sound
dumb. but I guess I am about that. Trying to figure out clays from
descriptions has always stumped me. I usually just test them out to see how
I like them.

I also have the option of using a clay that I have and just adding
grog/sand/kyanite to it. That might be easier. I have one clay that's
described as having 9% fine grog in it already. Maybe I could just buy
grogs and add to that but I would rather just buy one ready made.

Thanks,
Crystal
USA




|I have always recommended that people in your situation or a similar
| one, use a really coarse Stoneware/Raku clay, BUT overlay it with a slip
| made out of the SAME clay minus the grog.
|
| That way you have a body that can handle thermal shock, but at the same
| time have a surface that you can burnish to a high gloss if you wish to.
|
| The same technique can be used if a clay with a high colour is needed,
| for example a blue or black.
|
| To put loads of expensive oxides in a body when only the surface 3
| percent is visible at any one time seems to me to be fairly pointless,
| quite apart from the effect of a lot of fluxing oxide has on the whole
| piece!
|
| A good coat of slip can work wonders and open many technique options.
|
| Steve
| Bath
| UK
|
|
|
| >Hi,
| >
| >I make smoke fired pottery and have always bisque them at a low bisque
| >temperature but I'm looking for alternatives for people that I know do
not
| >own a kiln. I'm planning on doing some smoke-fired burnished pottery
pieces
| >and I'm wondering what I should start to look for in a clay if I am NOT
| >going to pre-bisque the pieces. Should I look for a clay that contains
grog,
| >sand or a combination? If so what should the mesh size be and what
| >percentage should be in the clay? Should it be earthenware or stoneware
or
| >does that matter? Would my best bet be for a raku clay? If someone out
there
| >only knows the name brand of the clay I could probably look the
information
| >up but I only have a couple brands available in my area. I know I could
| >contact them but I would prefer information from people that know about
it
| >first hand.
| >
| >I know that I have to worry about thermal shock and pieces breaking but I
do
| >have some ideas on how to remedy that if it does happen. This will be an
| >experimentation in itself, but my thinking is if I start with the best
clay
| >for this type of work the breakage should be reduced. Any and all
| >information would be greatly appreciated. Feel free to reply to me
directly.
| >
| >Thanks,
| >Crystal
| >
| >
| >
| >
|
| --
| Steve Mills
| Bath
| UK



Posted by Steve Mills on August 29, 2006, 12:47 pm
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Dear Crystal,

If you are going to bisque, I suggest no higher than 1450F (800C),
that way you retain any burnishing, and the clay will still accept the
effects of the pit fire. Above that, the bisque'd ware is almost immune
to change until you get to near stoneware.

Coarse clay I would define as anything with about 20 plus percent mixed
grog/Kyanite in it, a good spread of different sizes would be best. I am
a great fan of Kyanite; its structure makes it ideal for this sort of
work, as it almost *locks* everything together. I remember some
monumental Raku work by Susan & Stephen Kemenyffy, which stayed in one
piece due to a fair amount of this amazing stuff. However Kyanite makes
clay containing it a bit uncomfortable to throw!!

Your 9 percent clay would benefit from the addition of about 11 percent
heavy grog.

I would avoid using sand; I've always had problems with sanded clays in
Raku and pit firings. It might be me or the way I fire, but that's my
experience.

Have fun.

Steve
Bath
UK



>Hi Steve,
>Thanks for your reply. I figured I'd have to use the slip. Guess I was
>hoping for some magic bullet. The one I'm using doesn't really need the slip
>but I also bisque it first. That is true that we will have more options of
>decoration. I'll just have to find the time to make the slip before we have
>our get together. We would have more fun with it though.
>
>Can you define "course" for me? As in, what percentage and mesh sizes of
>grog/sand/kyanite that would make a"course" clay? I'm looking at two
>different suppliers and they're not all described like that. I don't know
>what percentages and mesh sizes I should consider "course". Hate to sound
>dumb. but I guess I am about that. Trying to figure out clays from
>descriptions has always stumped me. I usually just test them out to see how
>I like them.
>
>I also have the option of using a clay that I have and just adding
>grog/sand/kyanite to it. That might be easier. I have one clay that's
>described as having 9% fine grog in it already. Maybe I could just buy
>grogs and add to that but I would rather just buy one ready made.
>
>Thanks,
>Crystal
>USA
--
Steve Mills
Bath
UK

Posted by CNB on August 29, 2006, 2:04 pm
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The reason I'm asking about the clay is because we will be smoke firing
burnished greenware. I usually bisque mine and it works fine with the clay I
use, but I'm looking to help out a group of people that do not own a kiln
and still want to make pottery. That's why I want a clay that's most
resistant to thermal shock. They won't be throwing so I will use kyanite and
grog. You've confirmed my thought about the sand. I was leaning more towards
grog but I wasn't sure if that was the right way to go. I think this will
help a lot. Thank you so much!

Crystal



| Dear Crystal,
|
| If you are going to bisque, I suggest no higher than 1450F (800C),
| that way you retain any burnishing, and the clay will still accept the
| effects of the pit fire. Above that, the bisque'd ware is almost immune
| to change until you get to near stoneware.
|
| Coarse clay I would define as anything with about 20 plus percent mixed
| grog/Kyanite in it, a good spread of different sizes would be best. I am
| a great fan of Kyanite; its structure makes it ideal for this sort of
| work, as it almost *locks* everything together. I remember some
| monumental Raku work by Susan & Stephen Kemenyffy, which stayed in one
| piece due to a fair amount of this amazing stuff. However Kyanite makes
| clay containing it a bit uncomfortable to throw!!
|
| Your 9 percent clay would benefit from the addition of about 11 percent
| heavy grog.
|
| I would avoid using sand; I've always had problems with sanded clays in
| Raku and pit firings. It might be me or the way I fire, but that's my
| experience.
|
| Have fun.
|
| Steve
| Bath
| UK
|



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