Craig Martell on sat 2 aug 03
Hey:
Many thanks to David, Jim, and Ron for responding to my porcelain posts and
sharing some ideas and experience. I have to agree that some dilatometry
is necessary to get a definite answer to the fusion/expansion question.
I'm also trying some 250 mesh quartz from US Silica. The only sort of
toothy addition, besides molochite, to a porcelain body is spar and
quartz. I've tried some bodies with ultra fine quartz and the working
properties suffer, in my opinion. So I'm trying variations of 200 mesh US
Silica (bag number is silica #90) and 250 mesh silica (bag number is silica
#250). I'm interested in seeing if the working properties improve with a
larger mesh quartz. The caveats are, as Jim mentioned, deformation,
problems in the matrix, glaze fit, fusion, etc. I'll be testing this stuff
for many firings before I can come to any conclusions. Just thought I'd
mention this.
regards, Craig Martell Hopewell, Oregon
Craig Martell on sun 3 aug 03
Hello David:
Looking forward to throwing the Babu. They're telling me that I'll be
coming to Boulder in September or October at the latest. I promise not to
say anything at all about tech stuff. I'll just make pots.
regards, Craig Martell Hopewell, Oregon
Roger Korn on sun 3 aug 03
Craig Martell wrote:
> ... I'm interested in seeing if the working properties improve with a
> larger mesh quartz. The caveats are, as Jim mentioned, deformation,
> problems in the matrix, glaze fit, fusion, etc. I'll be testing this
> stuff
> for many firings before I can come to any conclusions. Just thought I'd
> mention this.
I also wonder if the rate of crystobalite formation depends on silica
mesh size.
Any ideas? Wish I had a dilatometer - I'd love to actually see that
shrinkage "jump" at
the quartz phase-change temps.
Roger
>
>
> regards, Craig Martell Hopewell, Oregon
>
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David Beumee on sun 3 aug 03
8/2/03 10:19:39 PM, Craig Martell wrote:
>I'm also trying some 250 mesh quartz from US Silica. The only sort of
>toothy addition, besides molochite, to a porcelain body is spar and
>quartz.
I hope you'll come to Colorado and try this Babu I mixed for you, as
there is a kind of tooth to the body just because of 55% Grolleg in
the mix; something about the ultra shortness of the clay perhaps.
Very nice indeed.
David Beumee
>Hey:
>
>Many thanks to David, Jim, and Ron for responding to my porcelain posts and
>sharing some ideas and experience. I have to agree that some dilatometry
>is necessary to get a definite answer to the fusion/expansion question.
>
>I'm also trying some 250 mesh quartz from US Silica. The only sort of
>toothy addition, besides molochite, to a porcelain body is spar and
>quartz. I've tried some bodies with ultra fine quartz and the working
>properties suffer, in my opinion. So I'm trying variations of 200 mesh US
>Silica (bag number is silica #90) and 250 mesh silica (bag number is silica
>#250). I'm interested in seeing if the working properties improve with a
>larger mesh quartz. The caveats are, as Jim mentioned, deformation,
>problems in the matrix, glaze fit, fusion, etc. I'll be testing this stuff
>for many firings before I can come to any conclusions. Just thought I'd
>mention this.
>
>regards, Craig Martell Hopewell, Oregon
>
>______________________________________________________________________________
>Send postings to clayart@lsv.ceramics.org
>
>You may look at the archives for the list or change your subscription
>settings from http://www.ceramics.org/clayart/
>
>Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
>
Ron Roy on tue 5 aug 03
Hi Roger,
It certainly does - micro crystalline quartz does convert to cristobalite
and should be avoided in stoneware bodies - or there should be enough KNaO
to melt it - Peter Sohngen certainly proved that in his experiments.
He also felt it necessary to have some cristobalite to help control crazing
- and adds some microfine silica to make sure it's there - a part of his
argument that I disagree with by the way. He is a casserole maker and
having any cristobalite in oven ware is asking for trouble. I say - make
the glazes fit the body and keep the cristobalite out.
All this is beside the point when it comes to porcelain - if it's fluxed
with feldspar there will be no cristobalite. The way to control
cristobalite is to melt it as it forms - so any body with 20 to 25% spar
will not have any - even if the body has 25% microfine silica - and even if
it is not fully fused.
By the way - our book has a couple of body charts in it.
I could show you all kinds of charts - especially raw clays - no flux -
massive cristobalite humps along with quarts humps - lots of charts in the
Sohngen article - quartz and cristobalite
RR
>I also wonder if the rate of crystobalite formation depends on silica
>mesh size.
>Any ideas? Wish I had a dilatometer - I'd love to actually see that
>shrinkage "jump" at
>the quartz phase-change temps.
>
>Roger
>
>>
>>
>> regards, Craig Martell Hopewell, Oregon
>>
>>
>>__________________________________________________________________________
>>____
>>
>> Send postings to clayart@lsv.ceramics.org
>>
>> You may look at the archives for the list or change your subscription
>> settings from http://www.ceramics.org/clayart/
>>
>> Moderator of the list is Mel Jacobson who may be reached at
>> melpots@pclink.com.
>>
>
>______________________________________________________________________________
>Send postings to clayart@lsv.ceramics.org
>
>You may look at the archives for the list or change your subscription
>settings from http://www.ceramics.org/clayart/
>
>Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
Ron Roy
RR#4
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Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
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