The name of the clay would be on the bag. Sounds like Raku - modelling
variety to me. I hate the stuff. I have seen more disasters using that
than with any other. It's OK for small, fairly thick items, bisque fired,
ready for a Raku Party. When you go into thinnish walled teapots, bottoms
crack off, appendages crack, and I have seen tiles go into flaking mode. If
it is not Raku, the clay suppliers will be only too happy for you to send
them a lump, so that they can do a test firing to suss out the problem and
refund if it is faulty.
"Eddie Daughton" wrote in message
...
When you use the hot air gun do you keep it + the pot moving? Gun up and
down pot round + round? so that no area gets too hot? Just a thought.....
Hugs
Eddie
"Bob Masta" wrote in message
...
On Wed, 24 Nov 2004 19:41:26 GMT, "JM" wrote:

Hi all,
I have a problem which has left myself, and my pottery teacher as puzzled
as
the pots.

Recently my ware has developed fine hairline cracking during bisque
firing.

All ware is thoroughly dried before firing (when pots are both fired at
college and at home) - so I don't damp is not the problem. One of the
items
has been on the drying shelf for about 2 months!

I have been using a hot-air gun to get some pieces to leatherhard stage
for
turning, but have not held it too close - I know a potter who even uses a
blow torch. So I am not even sure that this is the problem creater.

Thinking that when glazing the glaze might seep in and seal the fine
cracking, but the second firing being hotter opens them up even more.

The cracks are not localised and run in all directions, so are not caused
by
lack of compression.

If I can't get to the bottom of this irritating and frustrating condition
I
could always start a line in jigsaw pots.

Please come up with suggestions of possible causes - as I have exausted
all
known possibilities.

JM



Just a thought, but try skipping the hot air gun on a few
pieces. I'd guess that drying the surface much faster
than the interior must be building up some stress.

If this turns out to be the problem, then the next question
is how other folks get away with it. Different bodies?
Or maybe some technique difference with the hot air gun?
It might even be that a torch would work better than the
gun by drying only a very thin layer very quickly, not
penetrating quite so deeply.

Just a thought....



Bob Masta
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