Jonathan Kaplan on thu 28 nov 96
I'd like to suggest that while all of the posts on this subject have
touched on some important points that may help eliminate this problem, what
has been left out, and of course I'll add it in here, is that the most
overlooked subject that has perhaps a singular importance of great
magnitude is how we dry our ware. And this is also a function of the clay
body that is usedas well as the forming method.
For instance, bodies that are high in very fine particle sized materials
(read particle size, not mesh) such as ball clays, need to air dry longer
as they hold more water between the clay particle. One of the reasons that
coarser materials are added is to increase that space so that the water can
more freely move to the surface of the ware and evaporate.
I formulated a body many years ago that is now used by many of my
colleagues that is very high in fine particle sized materials, yet is
bullet proof. It can be dried with freshly pulled handles, in front of a
fan, with no cracking. No joke. It works. The secret is using materials
from a broad spectrum of fine particle sizes, proper material selection,
and of course, my alltime best material in the world, pyrophyllite. Yes
folks, this stuff is just the goods, and I have used it for more years than
I can remember as a substitute for all of the flint or part of the flint
and spar mix in the body. I have used it at most temperature ranges and it
imparts some wonderful properties to the body.
So along with the make up of the clay, how it is dried is so very
important. I dry all my jiggered open forms as well as thrown open form
upside down to equalize the drying between the foot and the rim, as the rim
will always dry first and sets up a stress, caused by differential moisture
which then translates into a differential shrinkage and voila, warpage. The
upside down drying thing works for me. I also bisque fire all my open forms
upside down or boxing them so that the rims are on as flat a surface as
possible.
"Ceramic Science for the Potter" by Lawrence as well as Tichane's "Clay
Bodies" are excellent, readable, and understandable references dealing with
clays, warpage, the clay water relationship, the water hull concept, all
these things that are directly related to drying. Basically, I can say that
if the pot is dried correctly, (assuming that the body is correct and the
firings are correct and the ware has not been mishandled as well as
hundreds of other variables,) the pot won't warp.
Jonathan
Jonathan Kaplan
http://www.craftweb.com/org/jkaplan/cdg.shtml
(aka "Scooter)
jonathan@csn.net
Ceramic Design Group Ltd./Production Services Voice:
970-879-9139 POB 775112
FAXmodem: same
Steamboat Springs, Colorado 80477, USA CALL before faxing
"Arrive on time, tell the truth, be a good listener, and don't
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humor!"
Donald G. Goldsobel on tue 17 dec 96
At 11:10 AM 11/28/96 EST, you wrote:
>----------------------------Original message----------------------------
>>I formulated a body many years ago that is now used by many of my
>colleagues that is very high in fine particle sized materials, yet is
>bullet proof.
Hey Scooter! Would you care to share this clay body? If can get the
equipment, I'm ready to find a single closed clay body I can mix myself.
Cone 8-11 maturity.
Thanks a heap.
Donald "Pots" Goldsobel in the San Fernando Valley.
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