Malone & Dean McRaine on thu 8 jul 99
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Aloha all:
Apparently I need to clarify some of my points about the raw glazing
methods I use. I want to say again that I'm a trial =26 error kind of guy =
and
these are the methods that I have worked out for the clay I use. The
interaction of dry (or leatherhard) clay and wet glaze should, I think, be
explored through experimentation for your specific clay and glaze.
Speaking of clay I posted a query a couple of weeks ago about clay bodies
for glazing raw and got no responses, I was having trouble with Laguna's
'S-60' stoneware, it fell apart rather easily when glazing. I got no
response so I talked to the clay guy at Laguna and we arrived at an
educated guess that the S-60 was too open, the water from the glaze went
right through in a short time and weakened it. 'Dave's porcelain' the other
body I use a lot is tighter and I have no problems with it. The lesson
being that some clay bodies are more suitable for raw glazing than others.
So here are some responses to other issues raised in the Clausens' post..
=22I can recall pouring slip into the inside of bonedry greenware and as it
dryed, I saw the pot spring with hundreds of cracks. Did not repeat
proceedure, rather always use slips on wetter greenware.=22
There's a few questions here. How thick was the slip, how long did you
leave it in the pot, does your clay body have good dry strength?? When you
wet bone dry clay with slip or glaze the wetted surface expands. I glaze
the outside of a piece first so that the expansion of the outside surface
compresses the inside, which can't break easily from a little squeeze,
rather than do the inside first and thereby expanding the outside and
possibly cracking the dry surface. It sounds like this is what happened to
you in this case. It's all about how the water from the glaze stresses the
clay as it soaks into it.
=22I am interested by the writtings of Dean, on converting bisqued to a
single fire glaze.
=22Just take a bone dry piece and dunk it in your glaze or spray it=22
Does it now crack up? If not, why did it do so with slip? Because the
slip is thick and clay-ey, greedy for water, and maybe absorbs more than
the more watery glaze? My imagination working hard..a very hazardly =
guess.=22
and..
=22Avoid glazing inner and outer surfaces at the same time=22 That sounds
different from the above, =22just dunk it your glaze=22.=22
I'm talking about dipping just the outside of a piece as an initial
experiment. If no flaws develop pour the inside after a short wait (10+
min) and see what happens. Very thick glazes or slips have more water to
soak into the dry pot and stress it and cause problems. The less water that
the dry pot has to handle at a time the safer the process is. That's why
spraying is the best method, spraying puts very little water into a pot and
it is a gradual process. Dipping is more abrupt but much better for
production work. Some raw glazers deflocculate their glazes in order to
have the least amount of water in the glaze. I don't in most cases but
it's a good idea.
=22Also Dean say also that =22most of the flaws that I=F8ve encountered show=
up
the time the glaze is dry on the pot=22
Do you mean the pot sprang?=22
The most typical flaws are cracks and bubbles that appear where the clay is
very thin (1/16=22 for my clay) or there are thick wet spots in the glaze
that overload the pot with water, where the glaze has pooled in the bottom
of a bowl, for instance. It usually only takes a minute or two for any
flaws to appear.
Good luck,
Dean
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