Bob Johnson on thu 14 dec 06
I want try my local black clay as a slip glaze, but it cracks and
falls off the pot when it dries. Any suggestions on additives that
might help reduce the dry shrinkage?
Bob Johnson - in Oregon
Paul Herman on fri 15 dec 06
Hello Bob,
Try calcining (bisque firing) half of the glaze material. You may
need to crush and screen the calcined material before making it into
glaze. That should reduce the drying shrinkage considerably.
Best,
Paul Herman
Great Basin Pottery
Doyle, California US
http://greatbasinpottery.com
On Dec 14, 2006, at 11:25 PM, Bob Johnson wrote:
> I want try my local black clay as a slip glaze, but it cracks and
> falls off the pot when it dries. Any suggestions on additives that
> might help reduce the dry shrinkage?
>
> Bob Johnson - in Oregon
Tommy Humphries on fri 15 dec 06
it is shrinking and falling off because of the high water content required
to make the clay into a slip.
try calcining the clay to 1500 deg. or so and ball milling the batch. you
can use cmc or other gums to help suspend/adhere the slip glaze to the pot.
also, heating the bisque ware to make the glaze dry really quickly may help.
tommy humphies
----- Original Message -----
Subject: local clay as slip glaze
> I want try my local black clay as a slip glaze, but it cracks and
> falls off the pot when it dries. Any suggestions on additives that
> might help reduce the dry shrinkage?
>
> Bob Johnson - in Oregon
Paul Borian on thu 21 dec 06
i have been using slip glazes for several years and they are now the basis
of my main product line, and i am still finding new variations. I built a
30 gallon prop-mixer so i can mix large batches and it does a great job of
slaking the clay down as long as it first broken down into smaller chunks.
I solved the glaze cracking problem a long time ago by adding cmc powder,
lots of it. As was already mentioned, you do have to be careful with water
content - it takes a lot of water to slake it down so you often have to
wait a while and skim some of the excess water off. If you let it get too
thick then you have the same problem again so it has to be just right.
Basically just add cmc powder or a similar binder until the problem goes
away.
i can get iron reds, temnoku and amber celedons with my slip glaze
depending on how i mix it and just recently i started even getting bluish
tints on thick areas using a combination of red and black iron oxide.
Paul
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