David W McDonald on sat 28 aug 99
Jonathan Kaplan,
Thanks so much for your e-mail. I would encourage you to post it
to the list if you're comfortable with that idea, as I think others could
benefit from what you said. But only if you're comfortable and willing.
I've received so many e-mails from folks with information I wish that
all could see.
I really appreciate the offer to help with body fomulation. I
doubt if I will go the route of mixing my own body here, as my studio is
small, I don't have room for the extra equipment, and I'd really rather
leave that kind of work to someone else. I don't have any apprentices or
helpers at the moment either. I know that trusting the clay mixing to
someone else puts me at risk to face this kind of ordeal again. But if
there's anything I've learned out of this experience, it's to stay atuned
to what's going on with the people I've put my trust into. A smaller
outfit, like the one I've found in Albuquerque, is going to be easier to
connect with when it's time to order more clay.
I'm sure that they would mix a special body for me. Could you
recommend a formula or two that you think might work well for the kind of
pieces I'm producing these days? I'm making platter/wallpieces which
range from 15" dia. to 25". I start off with a rolled slab which I drape
over a plaster hump form which is centered on the wheel ( a bat is
embedded into the bottom of the plaster, into which I've drilled holes to
match the wheelhead pins). I use a 4" roller to moderately compress the
slab onto the plaster form. Then I slip the slab at the midway point
between the center and the rim, so that I can add a coil for a footrim. I
add the coil and throw it on with the wheel turning, compressing the coil
into the slab and also compressing the whole back of the slab. I leave
these on the forms to dry for about a week in my damproom. The forms were
made by pouring plaster into a piece of cloth which is stretched over a
large wooden frame, kind of like a large painter's canvas, lying flat
across sawhorses. When poured into this stretched cloth, the weight of
the wet plaster pulls the cloth down, and depending on the give of the
fabric, goes to various depths. In essence these are catenary curves. The
shape is always determined by gravity. I think this really helps the
shape to maintain its form when going through the firing processes that
would normally cause some overhanging platter forms like this to slump.
They tend to keep their shapes nicely. As it dries, the clay releases
itself from the plaster form nicely too. I never have problems with
cracking, even on the big pieces, if I give them a week from forming to
being dry. With the Amador clay from Laguna, which I've discontinued
using, I have been able to stack these pieces in the bisque firing two
high without any problems as long as I fire long and slow. The occasional
piece will come out of the bisque with one or more fine cracks in the
footrim. So far I have been able to tolerate these loses, as they were
few. However, with the "Anasazi" body which I like so much from
Albuquerque, these fine cracks in the footrims are showing up at a much
higher rate, an unacceptable rate really if I can't get more to come out
without cracking. I've been bisquing to cone 06 for a period of 40 hours,
so I would think that it's not that I need to slow down the bisque. I'm
wondering if there's something in the body formulation that would
encourage this kind of work to bisque without cracking. I really like the
smoothness of the fired results of this body, and the way the glazes work
on it. I know that it has both sand and grog in it. I imagine that a
body with alot more grog would succeed better in these conditions, but I
would be disappointed to give up too much of the smoothness. Any ideas? I
hope I've told you enough about my forming processes to give you an idea
of what kind of a clay body might be good to try.
Once again Jonathan, thanks for your kind offer and respond to
this when you have time. Sincerely, David McDonald
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Craig Martell on sun 29 aug 99
David wrote:
>----------------------------Original message----------------------------
> However, with the "Anasazi" body which I like so much from
>Albuquerque, these fine cracks in the footrims are showing up at a much
>higher rate, an unacceptable rate really if I can't get more to come out
>without cracking. I've been bisquing to cone 06 for a period of 40 hours,
>so I would think that it's not that I need to slow down the bisque.
David:
Try raising your bisque temperature to 04. This may stop the cracking.
Craig Martell in Oregon
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