Michael McDowell on wed 14 oct 98
Fellow Clayarters,
I'm hoping that some of you may be in a position to help me with a project
I've been working on with Tony Hansen, the author of Insight glaze
calculation software. I'm guessing that some of you have Insight software,
and that some of you who do have already worked out a glaze or two that fits
a commercial clay body that you use. What I'm trying to do is put together a
database of information on the calculated thermal expansion of glazes that
fit various commercially available clay bodies. The idea is that we can
infer that the thermal expansion of each clay is fairly close to that of the
glazes that fit it. Sometimes we are not able to adjust glazes to fit the
clay bodies we use. Information on alternative bodies with different rates
of expansion could be quite useful, but as yet most clay manufacturers are
not providing such data. My idea is that together we could generate our own
pool of information on this subject.
If any of you think you might be able to help with this project, please take
a look at the start we've made on Tony's website. The full address of the
inferred expansion database project is:
http://www.digitalfire.com/education/clay/InferExp.htm
or you can navigate to it through Tony's homepage:
http://www.digitalfire.com
I've included data on a couple of clay bodies I use, and Tony's added a
Plainsman Clay, but this project has so far failed to get any submissions
other than that. I'd appreciate any submissions, or any clues as to how to
get them.
Thanks,
Michael McDowell
Whatcom County, WA USA
mmpots@memes.com
http://www2.memes.com/mmpots
Craig Martell on fri 16 oct 98
Hello Michael:
As you probably know, Jim Robinson wrote some articles for Studio Potter on
the this subject. "Fear of Silica" June 1981 and "Body Building for
Potters", June 1988. He gives receipes for 10 glazes, that run from high to
low expansion. One can use these glazes to extract information on whether
or not commercial bodies are balanced or not. I've used this series of
glazes to develop some stoneware bodies in the past and they work. I also
used them to demonstrate that a certain commercial body that was being used
at an art center I worked at was underfluxed and developing a lot of
cristobalite which led to many cracked mugs and teapots for the students.
The reason that I mention this series of glazes is that there are some
commercial bodies that aren't worth using because they are very unbalanced
and hard to fit glazes to among other problems. Once one finds a body that
is well formulated you could use this series of glazes to find the proper
expansion range for that particular claybody.
regards, Craig Martell-Oregon
Tom Constans on sat 17 oct 98
>----------------------------Original message----------------------------
>Hello Michael:
>
>As you probably know, Jim Robinson wrote some articles for Studio Potter on
>the this subject. "Fear of Silica" June 1981 and "Body Building for
>Potters", June 1988. He gives receipes for 10 glazes, that run from high to
>low expansion. One can use these glazes to extract information on whether
>or not commercial bodies are balanced or not. I've used this series of
>glazes to develop some stoneware bodies in the past and they work. I also
>used them to demonstrate that a certain commercial body that was being used
>at an art center I worked at was underfluxed and developing a lot of
>cristobalite which led to many cracked mugs and teapots for the students.
>
>The reason that I mention this series of glazes is that there are some
>commercial bodies that aren't worth using because they are very unbalanced
>and hard to fit glazes to among other problems. Once one finds a body that
>is well formulated you could use this series of glazes to find the proper
>expansion range for that particular claybody.
>
>regards, Craig Martell-Oregon
Craig
Would it be unsporsmanlike to name some well balanced commercial bodies
available from our NW sources? I'd appreciate suggestions in each firing
range ^04, ^6, ^10 from Geogies, ClayArt, SPC and Plainsman.
Tom Constans - Bellingham
Michael McDowell on mon 19 oct 98
Craig,
Thanks for reminding me of those articles:
"As you probably know, Jim Robinson wrote some articles for Studio Potter on
the this subject. "Fear of Silica" June 1981 and "Body Building for
Potters", June 1988."
I have heard of them, but never have gotten around to reading them. Do you
know if there is anyplace I could find those articles online? Ron Roy tells
me that he has done some testing for someone who is coming out with a new
article on silica in clay bodies as well. But all this doesn't seem to me an
alternative for the project I'm working on.
I have been able to fit glazes to my clay bodies, many glazes at least. I am
having difficulty with glazes high in iron and or rutile as these oxides are
highly expansive and my clay bodies are fairly low in expansion. My current
project on Tony Hansen's web site has to do with sharing this information
and pooling what I've found out about my clays with what others have found
out about theirs. That way, should any of us decide that we would like to
switch to a higher or lower expansion clay body, or switch to a clay with
different mechanical properties and similar expansion to what we've already
developed glazes for, there will be a resource available to help us choose
which clays we might want to try.
Such a pool of information was not even feasible before the advent of glaze
software made it simple to determine the approximate expansion of the glazes
we use. But once the data is assembled, it will be useful to many potters
regardless of whether or not they use glaze software themselves. If we get
enough potter's reporting the expansion of glazes they have found to fit
various commercially available clays, it should be possible to establish an
ordinal ranking of the clays available in the marketplace, from the least to
the most expansive. This information should be useful to anyone
contemplating a change in clays either to solve problems with glazes or to
achieve different affects without creating glaze fit problems.
Michael McDowell
Whatcom County, WA USA
mmpots@memes.com
http://www2.memes.com/mmpots
Craig Martell on tue 20 oct 98
>Thanks for reminding me of those articles:
>I have heard of them, but never have gotten around to reading them. >Do you
know if there is anyplace I could find those articles online
Hello Michael:
No, I don't know if they are available on the net. Knowing Jim, they
probably aren't. I can get Studio Potter back issues to read here at the
public library. You might give that a shot.
regards, Craig Martell in Oregon
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