Jason Mongue on tue 6 jul 04
Hi all. I ran a couple glaze fit tests in my last glaze fire and am a bit
curious of the results. I'm using the expansion test glazes from Mastering
Cone 6 Glazes, and made up a five part line blend from the lowest expansion
test glaze to the glossy base glaze listed in the back of the book, which
is listed as somewhere between the lowest exp and the second lowest exp
glaze tests. The calculated expansion (using GlazeMaster) of the lowest is
62.90 and the one at the other end of the tests is 65.90. On my test
pieces, all five tests show lots of cracks. Is there a way to tell if the
cracks in my test pieces are due to crazing vs shivering? None of the
glaze has chipped off, but at the same time I'm wondering if it's really
possible that my clay body has a lower expansion than the lowest expansion
glaze test they list in their test suite for expansion.
My next step is to run the full range of expansion tests, but while I'm
making enough pieces to fill another glaze load, I thought I'd check with
the potters out there to maybe shed some light and wisdom on the data I've
got so far.
Thanks,
Jason
David Beumee on thu 8 jul 04
Hi Jason,
If I'm understanding correctly, isn't your object to find out if the present clay body you're using has good glaze fit? If this is what you're after, why are you doing a line blend? Ron and Jon have already carefully calculated the five cone 6 glazes from low to high expansion so that you can simply make up the five glazes and try each of them on test mice from the body that you're presently using. If your body is of low enough expansion to put enough compression on the lowest expansion of the glaze test series to cause shivering, you could try adding percetages of silica to the body to raise its expansion. Good light and a magnifying glass are sometimes very helpful to see shivering.
David Beumee
Earth Alchemy Pottery
Lafayette, CO
> Hi all. I ran a couple glaze fit tests in my last glaze fire and am a bit
> curious of the results. I'm using the expansion test glazes from Mastering
> Cone 6 Glazes, and made up a five part line blend from the lowest expansion
> test glaze to the glossy base glaze listed in the back of the book, which
> is listed as somewhere between the lowest exp and the second lowest exp
> glaze tests. The calculated expansion (using GlazeMaster) of the lowest is
> 62.90 and the one at the other end of the tests is 65.90. On my test
> pieces, all five tests show lots of cracks. Is there a way to tell if the
> cracks in my test pieces are due to crazing vs shivering? None of the
> glaze has chipped off, but at the same time I'm wondering if it's really
> possible that my clay body has a lower expansion than the lowest expansion
> glaze test they list in their test suite for expansion.
>
> My next step is to run the full range of expansion tests, but while I'm
> making enough pieces to fill another glaze load, I thought I'd check with
> the potters out there to maybe shed some light and wisdom on the data I've
> got so far.
>
> Thanks,
> Jason
>
> ______________________________________________________________________________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
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Dave Finkelnburg on thu 8 jul 04
----- Original Message -----
From: "Jason Mongue"
To:
Sent: Tuesday, July 06, 2004 1:34 PM
Subject: shivering vs. crazing test
> Hi all. I ran a couple glaze fit tests in my last glaze fire and am a bit
> curious of the results. I'm using the expansion test glazes from
Mastering
> Cone 6 Glazes, and made up a five part line blend from the lowest
expansion
> test glaze to the glossy base glaze listed in the back of the book, which
> is listed as somewhere between the lowest exp and the second lowest exp
> glaze tests. The calculated expansion (using GlazeMaster) of the lowest
is
> 62.90 and the one at the other end of the tests is 65.90. On my test
> pieces, all five tests show lots of cracks. Is there a way to tell if the
> cracks in my test pieces are due to crazing vs shivering? None of the
> glaze has chipped off, but at the same time I'm wondering if it's really
> possible that my clay body has a lower expansion than the lowest expansion
> glaze test they list in their test suite for expansion.
>
> My next step is to run the full range of expansion tests, but while I'm
> making enough pieces to fill another glaze load, I thought I'd check with
> the potters out there to maybe shed some light and wisdom on the data I've
> got so far.
>
> Thanks,
> Jason
>
>
____________________________________________________________________________
__
> 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.
Dave Finkelnburg on thu 8 jul 04
Jason,
Is your clay body a white body, a sort of porcelain, or an iron-bearing
stoneware? The cracks certainly indicate crazing, which favors the idea
that your clay body is low in expansion, as most porcelains are. Most
stoneware would shiver a glaze at the low end of your tests, but you usually
won't see cracking until the glaze chips off. The shivering will show first
on sharp outside corners. It is good to have such edges on your test tile,
just to check for shivering. Cracking on smooth, flat surfaces is probably
an indication of crazing.
Regards,
Dave Finkelnburg
----- Original Message -----
From: "Jason Mongue"
Sent: Tuesday, July 06, 2004 1:34 PM
> Hi all. I ran a couple glaze fit tests in my last glaze fire and am a bit
> curious of the results. I'm using the expansion test glazes from
Mastering
> Cone 6 Glazes, and made up a five part line blend from the lowest
expansion
> test glaze to the glossy base glaze listed in the back of the book, which
> is listed as somewhere between the lowest exp and the second lowest exp
> glaze tests. The calculated expansion (using GlazeMaster) of the lowest
is
> 62.90 and the one at the other end of the tests is 65.90. On my test
> pieces, all five tests show lots of cracks. Is there a way to tell if the
> cracks in my test pieces are due to crazing vs shivering? None of the
> glaze has chipped off, but at the same time I'm wondering if it's really
> possible that my clay body has a lower expansion than the lowest expansion
> glaze test they list in their test suite for expansion.
David Beumee on sat 10 jul 04
Hi Jason,
If it turns out that none of Ron and Jon's glaze test series fit your body, you might consider raising or changing the expansion of your clay body rather than trying to come up with glazes that are super low expansion. You never know when you might find a glaze you'd like to try, and it's a hassel having to constantly lower expansion rates of glazes to fit your super low expansion body, unless of course you're specifically going for a low expansion body for ovenware reasons. There aren't any shortcuts around using either Ron and Jon's GTS (glaze test series) for cone 6 or Jim Robinson's GTS for cone 10, and it's some work to make up all five (or all ten) glazes, but then you have an excellent baseline to work from.
David Beumee
Earth Alchemy Pottery
Lafayette, CO
> Hi David. Thanks for responding to my post. Well, the reason I did the
> line blend was because I haven't yet done the full set of five expansion
> test glazes. I tried to take a short cut, assuming my clay body was very
> low expansion. I had already done some glaze tests with their base glossy
> glaze which crazed (or at least had cracks in it). They said their base
> glossy glaze fell (expansion wise) between their lowest expansion test glaze
> and next one up. So the next thing they recommend doing is running a line
> blend between their two lowest expansion glazes and finding where the
> crazing stops. I effectively did this, though I used the base glossy as the
> higher expansion end rather than the one in the expansion test chapter. The
> weird part is that all five (of my low expansion tests) have cracks in them.
> Given their lowest expansion test had cracks on my clay, and the fact
> that they say they've never come across a claybody where the lowest
> expansion test crazed, it makes me wonder if the cracks I'm seeing are
> actually indicative of mild shivering. Unfortunately, none of the glaze is
> flecking off, so I can't definitively say if it's shivering or crazing.
>
> So, my next step is to go back to the drawing board and run their full set
> of five tests. I have a bad suspision though that the clay body I'm using
> really is an even lower expansion clay than their lowest expansion test,
> which means I may have to reformulate their lowest expansion glaze test to
> be even lower to fit my clay..
>
> Jason
>
>
>
> >From: claybuds@att.net
> >To: Clayart
> >CC: Jason Mongue , CLAYART@LSV.CERAMICS.ORG,
> >Subject: Re: shivering vs. crazing test
> >Date: Thu, 08 Jul 2004 05:20:02 +0000
> >
> >Hi Jason,
> > If I'm understanding correctly, isn't your object to find out if the
> >present clay body you're using has good glaze fit? If this is what you're
> >after, why are you doing a line blend? Ron and Jon have already carefully
> >calculated the five cone 6 glazes from low to high expansion so that you
> >can simply make up the five glazes and try each of them on test mice from
> >the body that you're presently using. If your body is of low enough
> >expansion to put enough compression on the lowest expansion of the glaze
> >test series to cause shivering, you could try adding percetages of silica
> >to the body to raise its expansion. Good light and a magnifying glass are
> >sometimes very helpful to see shivering.
> >
> > David Beumee
> > Earth Alchemy Pottery
> > Lafayette, CO
> >
> >
> > > Hi all. I ran a couple glaze fit tests in my last glaze fire and am a
> >bit
> > > curious of the results. I'm using the expansion test glazes from
> >Mastering
> > > Cone 6 Glazes, and made up a five part line blend from the lowest
> >expansion
> > > test glaze to the glossy base glaze listed in the back of the book,
> >which
> > > is listed as somewhere between the lowest exp and the second lowest exp
> > > glaze tests. The calculated expansion (using GlazeMaster) of the lowest
> >is
> > > 62.90 and the one at the other end of the tests is 65.90. On my test
> > > pieces, all five tests show lots of cracks. Is there a way to tell if
> >the
> > > cracks in my test pieces are due to crazing vs shivering? None of the
> > > glaze has chipped off, but at the same time I'm wondering if it's really
> > > possible that my clay body has a lower expansion than the lowest
> >expansion
> > > glaze test they list in their test suite for expansion.
> > >
> > > My next step is to run the full range of expansion tests, but while I'm
> > > making enough pieces to fill another glaze load, I thought I'd check
> >with
> > > the potters out there to maybe shed some light and wisdom on the data
> >I've
> > > got so far.
> > >
> > > Thanks,
> > > Jason
> > >
> > >
> >______________________________________________________________________________
> > > 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.
>
> _________________________________________________________________
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