Joy Holdread on fri 23 oct 98
Greetings all,
Last kiln load I fired many small pieces of black clay with a porcelain slip
over. Single fire to cone 8. As I recycle clay from various sources clays I
can't be specific on the clay body. Some bloated most didn't. What might be
the causes?
1. Pieces in heavier reduction areas of kiln? I don't actually reduce but I
fire gas & occasionally see some spot reductions depending on the stack.
2. Some of the slip molded. Extra organics in the burn out.
3. I skim off & screen extra water to make slip when I recycle, perhaps this
was a batch on incompatible slip.
4. The dark clay did an iron thing sometimes?
5. Is there any stage of slip application that may cause bloating.
6. Your input please
Joy in Tucson
meanwhile I'm retesting every slip on 3 colors of clay in different places in
the kiln, some bisque some single fire.
Thanks for insights
Craig Martell on mon 26 oct 98
>----------------------------Original message----------------------------
>Greetings all,
>Last kiln load I fired many small pieces of black clay with a porcelain
slip
>over. Single fire to cone 8. As I recycle clay from various sources clays
I
>can't be specific on the clay body
Hello Joy:
Bloating is usually caused by overfiring or early fusion of the body that
will trap gasses formed in later stages of the firing. The clay has
tightened enough that the gasses can't escape and you get bloats. This is
an oversimplified account but I didn't want to put anyone to sleep,
especially myself. It's been a long day!
The only advice I can give you since the composition of the clay is unknown
is: Cut the recycling of various bodies and keep your clay uniform in
composition. The most expensive part of any studio operation is the
potter's TIME. Clay is inexpensive by comparison. Don't waste your time
and energy making pots out of recycled, unknown clay. I think that if you
continue to do this there will always be problems. If you don't know what
you've got, you can't arrive at a way to fix what's wrong. This probably
isn't what you wanted to hear but I guess all I can say is that my opinion
is offered in a constructive way and I'm not preaching at you about
anything.
hope you get it worked out, Craig Martell in Oregon
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