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cracking in large sculptural vessels

updated wed 15 sep 99

 

Rachael Rice on mon 13 sep 99

I have been building soft slab sculptures with high fired stoneware. I
work with soft slabs so that I can do more bending and sculpting of my
organic forms. Everytime I try to build structures larges that 15 in
tall or 8 inches wide I get alot of cracking. I form my slab around a
soft support, usually foam, in a lying down position on my work table. I
usually build it lying down on soft quilting batting. The cracking can
occur at various times. Sometimes just moments after I have finished
working with the piece to get it to the point I am happy with it and
have repaired all the weak craks and joints, I get a large pulling away
of the bottom of the structurethat is lying on the table from the sides.
It seems like the clay wants to go back to its flat form. Sometimes I
get the piece wrapped in plastic and check on it two hours later and the
cracking has occured in many different areas. I ususally dry in by
covering it with canvas cloth and then a couple layers of dry cleaning
plastic. It has been suggested that I am drying to slowly or drying to
fast or I need more grog in my clay . I find the heavily grogged clay
difficult to sculpt with. Nylon was suggested also but the only source
for nylon in clay requires a 1000lb. commitment to made up which I am
not sure I am ready for. I was also told the only way to cut clay with
nylon is with a scizzor. I have no problems with my clay structures if
I keep them under 15 inches but anything larger seems technically
problematic. I want to keep working with soft slabs. Any suggestions?
Rachael

-- Cheryl Pannabecker on tue 14 sep 99

I've made a lot of forms in a similar way to how you are doing it and haven't
encountered that problem. I agree with some of the answers you've already
been given. Have you tried adding the fine grog? I know you said you didn't
want to work with very groggy clay. I think the fine does not give the clay
a rough or groggy look.
Columbus Clay Co. sells nylon fibers in 5 lb. increments, so it is possible
to experiment with that. Their phone no. is 614-294-1114. I'm also
wondering if your clay is aged enough. It sounds "short". I have sometimes
received clay from the manufacturer that feels like it was made yesterday.
You can try soaking a rag with vinegar, covering your clay with it, let it
sit awhile and wedge it very well. Or, you can always experiment with other
clay bodies. When I make larger pieces, I build in an internal armature, but
your pieces sound like they're not to the size where that should be necessary.

Cheryl Pannabecker
Cincinnati, Ohio

John Fazzino on tue 14 sep 99

Rachel,
This seems difficult for me to envision. Your pieces are lying down so maybe
you need more support underneath them? Are edges suspended unsupported? I
would definitely go with a clay with more grog. Are you mixing yourself?
You could add sawdust as well if so. Can you work with pieces standing up?
Maybe you could use a soft clay form underneath as a support that could be
taken out when the clay is firm.
Good luck.
John Fazzino
In a message dated 9/13/99 2:18:28 PM, rachaelrice@erols.com writes:

<< I have been building soft slab sculptures with high fired stoneware. I
work with soft slabs so that I can do more bending and sculpting of my
organic forms. Everytime I try to build structures larges that 15 in
tall or 8 inches wide I get alot of cracking. I form my slab around a
soft support, usually foam, in a lying down position on my work table. I
usually build it lying down on soft quilting batting. The cracking can
occur at various times. Sometimes just moments after I have finished
working with the piece to get it to the point I am happy with it and
have repaired all the weak craks and joints, I get a large pulling away
of the bottom of the structurethat is lying on the table from the sides.
It seems like the clay wants to go back to its flat form. Sometimes I
get the piece wrapped in plastic and check on it two hours later and the
cracking has occured in many different areas. I ususally dry in by
covering it with canvas cloth and then a couple layers of dry cleaning
plastic. It has been suggested that I am drying to slowly or drying to
fast or I need more grog in my clay . I find the heavily grogged clay
difficult to sculpt with. Nylon was suggested also but the only source
for nylon in clay requires a 1000lb. commitment to made up which I am
not sure I am ready for. I was also told the only way to cut clay with
nylon is with a scizzor. I have no problems with my clay structures if
I keep them under 15 inches but anything larger seems technically
problematic. I want to keep working with soft slabs. Any suggestions?
Rachael >>

Dannon Rhudy on tue 14 sep 99


Rachel, you really do need a fibrous clay for what you are attempting.
You can make or buy paperclay, and it should serve your purposes.
Nylon fiber will do the same. If you cannot find chopped nylon from
your clay supplier, there are other sources. Try Alfred University,
they sell various things from their supply room, including chopped
nylon, which can be bought by the pound. It is not expensive, and
a pound goes a very long way.

If you are making your own clay, it is easy to incorporate either of
these fibers. Just add it to the mixer as you're making the clay.
If you are buying your clay ready-made, then you can
buy the paper clay. Many suppliers have it, or can get it. You can
wedge nylon fiber in yourself, I've done it before. Tiresome but possible.

Either of these should solve your cracking problems, unless the clay is
just too wet, thick, and ill-supported. Those problems would require a
rethinking of your construction techniques.

Regards,

Dannon Rhudy
potter@koyote.com




At 02:17 PM 9/13/99 EDT, you wrote:
>----------------------------Original message----------------------------
>I have been building soft slab sculptures with high fired stoneware. I
>work with soft slabs so that I can do more bending and sculpting of my
>organic forms. Everytime I try to build structures larges that 15 in
>tall or 8 inches wide I get alot of cracking. I form my slab around a
>soft support, usually foam, in a lying down position on my work table. I
>usually build it lying down on soft quilting batting. The cracking can
>occur at various times. Sometimes just moments after I have finished
>working with the piece to get it to the point I am happy with it and
>have repaired all the weak craks and joints, I get a large pulling away
>of the bottom of the structurethat is lying on the table from the sides.
>It seems like the clay wants to go back to its flat form. Sometimes I
>get the piece wrapped in plastic and check on it two hours later and the
>cracking has occured in many different areas. I ususally dry in by
>covering it with canvas cloth and then a couple layers of dry cleaning
>plastic. It has been suggested that I am drying to slowly or drying to
>fast or I need more grog in my clay . I find the heavily grogged clay
>difficult to sculpt with. Nylon was suggested also but the only source
>for nylon in clay requires a 1000lb. commitment to made up which I am
>not sure I am ready for. I was also told the only way to cut clay with
>nylon is with a scizzor. I have no problems with my clay structures if
>I keep them under 15 inches but anything larger seems technically
>problematic. I want to keep working with soft slabs. Any suggestions?
>Rachael
>