Paul Lewing on wed 12 dec 01
on 12/12/01 11:56 AM, Judith I. Marvin at judithimarvin@HOTMAIL.COM wrote:
> Here's the glaze.
>
> Cushing Satin Matt
> 20% Whiting
> 25 Frit 3134
> 25 Neph Sy
> 15 EPK
> 15 Silica
> add 10% Zircopax
Judith, you're right, the expansion is a bit high- 7.91 according to
Insight. I find I need an expansion around 6.8 to 7.1 for the clay I use
(also from Clay Art Center, but not this same clay).
There are several reasons for this. First, your fluxes are almost entirely
calcium and sodium, two of the highest expansion flux oxides (.75 CaO and
.21 Na2O). And, at 2.12, the SiO2 (one of the lowest expansion oxides) is
below the conventional limits for a stable glaze.
So what to do? I'd first add silica, maybe in 2% increments up to a total
of 25 or so. If that's not enough, I'd cut down the whiting, or replace
some or all of it with dolomite. That would cut down the CaO, and the
dolomite substitution would replace CaO with MgO, a low-expansion oxide.
The Na2O is the higher expansion oxide, but getting it out of the Neph Sy
without also subtracting stuff you need would be more complicated. At .75,
the CaO is outside normal limits anyway.
Good luck,
Paul Lewing, Seattle
Judith I. Marvin on wed 12 dec 01
Here is a query for those glaze gurus out there. I'm really showing my
ignorance here. I've been trying a glaze that I just love the look of, it
has a beautiful, buttery surface, is nice with either underglaze decoration
or oxides brushed on top. The problem is, I'm getting crazing. Assuming
that what I have is poor glaze fit what should I try to improve the fit
without changing the look of the glaze. The clay body I'm using is "Idaho
Buff" (with grog) from Clay Art Center in Seattle. Firing cone 6 oxidation.
Here's the glaze.
Cushing Satin Matt
20% Whiting
25 Frit 3134
25 Neph Sy
15 EPK
15 Silica
add 10% Zircopax
_________________________________________________________________
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Craig Martell on wed 12 dec 01
Hi:
This glaze has a high calculated expansion. That means it will most likely
craze on a lot of claybodies. It's over the limit with calcium and a bit
under the limit with silica.
An easy thing to try is lowering the whiting by 5%. This brings the silica
within limits and drops the calculated expansion of the glaze so you'd be
moving in the right direction. The alumina comes up when this is done so
it may change the character of the glaze a bit. You won't know until you
give it a try. This glaze is probably a cacium/borosilicate matt and
lowering the whiting may give it a bit more gloss too. Calcium matts are
nice because they are translucent and sometimes transparent so underglaze
work shows well. You could add magnesia to this glaze for a lower
calculated expansion but you'd sacrifice some transparency.
If the lower whiting doesn't stop the crazing, and it may not, there are
other measures that you can try too. So don't be discouraged if you need
to go further with remedies.
regards, Craig Martell in Oregon
John Hesselberth on wed 12 dec 01
Hi Judith,
The first thing I would try would be to raise the silica and alumina while
keeping the ratio of the two the same. Doing this should also improve the
durability of the glaze because it is low in both as it stands now. Just to
keep the numbers simple, I took EPK up 20 and silica to 22 holding every
thing else the same. This keeps the Si/Al ratio at about 7.3:1 and lowers
the calculated expansion from 85 to 80 (HyperGlaze). Calculating expansion
on satin mattes is not very accurate, though, so you may have to experiment
quite a bit to fix this one.
Renormalizing to a total of 100 would give a revised glaze recipe of:
Neph Sy 22.3
Frit 3134 22.3
Whiting 17.9
EPK 17.9
Silica 19.6
If you try it, let us know how it works.
Regards,
John
on 12/12/01 2:56 PM, Judith I. Marvin at judithimarvin@HOTMAIL.COM wrote:
> Here is a query for those glaze gurus out there. I'm really showing my
> ignorance here. I've been trying a glaze that I just love the look of, it
> has a beautiful, buttery surface, is nice with either underglaze decoration
> or oxides brushed on top. The problem is, I'm getting crazing. Assuming
> that what I have is poor glaze fit what should I try to improve the fit
> without changing the look of the glaze. The clay body I'm using is "Idaho
> Buff" (with grog) from Clay Art Center in Seattle. Firing cone 6 oxidation.
> Here's the glaze.
>
> Cushing Satin Matt
> 20% Whiting
> 25 Frit 3134
> 25 Neph Sy
> 15 EPK
> 15 Silica
> add 10% Zircopax
>
web sites: http://www.masteringglazes.com and http://www.frogpondpottery.com
EMail: john@frogpondpottery.com
"It is, perhaps, still necessary to say that the very best glazes cannot
conceal badly shaped pots..." David Green, Pottery Glazes
Ron Roy on thu 13 dec 01
Hi Judith,
You are right - the glaze contracts too much on cooling - more than the
clay so crazing is the result.
The expansion/contraction is high in this glaze - its a high calcium glaze
- short of silica as well so probably not stabe\le so it will probably not
hold colours well in use.
I recalculated it to lower the expansion but it may not look the same - but
then again it could also be better looking - anyway worth a try - ley us
know how it works.
Whiting - 17.0
Talc - 3.0
Frit 3134 - 27.0
Neph Sy - 9
EPK - 26.0
Silica - 18.0
Zircopax - 10.0
Total - 110.0
RR
>Here is a query for those glaze gurus out there. I'm really showing my
>ignorance here. I've been trying a glaze that I just love the look of, it
>has a beautiful, buttery surface, is nice with either underglaze decoration
>or oxides brushed on top. The problem is, I'm getting crazing. Assuming
>that what I have is poor glaze fit what should I try to improve the fit
>without changing the look of the glaze. The clay body I'm using is "Idaho
>Buff" (with grog) from Clay Art Center in Seattle. Firing cone 6 oxidation.
> Here's the glaze.
>
> Cushing Satin Matt
> 20% Whiting
> 25 Frit 3134
> 25 Neph Sy
> 15 EPK
> 15 Silica
> add 10% Zircopax
Ron Roy
RR# 4
15084 Little Lake Rd..
Brighton,
Ontario, Canada
KOK 1H0
Residence 613-475-9544
Studio 613-475-3715
Fax 613-475-3513
David Hewitt on thu 13 dec 01
Judith,
I would start by doing a progression blend on the silica, increasing the
amounts in steps of 5 to 20, 25, 30 and 35 parts and see what you get.
You may be interested in my article 'Calculating Crazing' which you can
see on my web site listed under the heading Pottery Techniques.
http://www.dhpot.demon.co.uk
David
In message , Judith I. Marvin writes
>Here is a query for those glaze gurus out there. I'm really showing my
>ignorance here. I've been trying a glaze that I just love the look of, i=
>t
>has a beautiful, buttery surface, is nice with either underglaze decorati=
>on
>or oxides brushed on top. The problem is, I'm getting crazing. Assuming
>that what I have is poor glaze fit what should I try to improve the fit
>without changing the look of the glaze. The clay body I'm using is "Idah=
>o
>Buff" (with grog) from Clay Art Center in Seattle. Firing cone 6 oxidati=
>on.
> Here's the glaze.
>
> Cushing Satin Matt
> 20% Whiting
> 25 Frit 3134
> 25 Neph Sy
> 15 EPK
> 15 Silica
> add 10% Zircopax
>
>
>
>_________________________________________________________________
>MSN Photos is the easiest way to share and print your photos:
>http://photos.msn.com/support/worldwide.aspx
--
David Hewitt
David Hewitt Pottery ,
7 Fairfield Road, Caerleon, Newport,
South Wales, NP18 3DQ, UK. Tel:- +44 (0) 1633 420647
FAX:- +44 (0) 870 1617274
Web site http://www.dhpot.demon.co.uk
Judith I. Marvin on thu 13 dec 01
Thank you Paul. I'll learn something about glaze chemestry yet. I find it
a bit intimidating but would do myself a favor try. Plan on working with
this one a bit. Thanks for the time of your reply. Judith
>From: Paul Lewing
>Reply-To: Ceramic Arts Discussion List
>To: CLAYART@LSV.CERAMICS.ORG
>Subject: Re: glaze fit
>Date: Wed, 12 Dec 2001 19:07:54 -0800
>
>on 12/12/01 11:56 AM, Judith I. Marvin at judithimarvin@HOTMAIL.COM wrote:
>
> > Here's the glaze.
> >
> > Cushing Satin Matt
> > 20% Whiting
> > 25 Frit 3134
> > 25 Neph Sy
> > 15 EPK
> > 15 Silica
> > add 10% Zircopax
>
>
>Judith, you're right, the expansion is a bit high- 7.91 according to
>Insight. I find I need an expansion around 6.8 to 7.1 for the clay I use
>(also from Clay Art Center, but not this same clay).
>There are several reasons for this. First, your fluxes are almost entirely
>calcium and sodium, two of the highest expansion flux oxides (.75 CaO and
>.21 Na2O). And, at 2.12, the SiO2 (one of the lowest expansion oxides) is
>below the conventional limits for a stable glaze.
>So what to do? I'd first add silica, maybe in 2% increments up to a total
>of 25 or so. If that's not enough, I'd cut down the whiting, or replace
>some or all of it with dolomite. That would cut down the CaO, and the
>dolomite substitution would replace CaO with MgO, a low-expansion oxide.
>The Na2O is the higher expansion oxide, but getting it out of the Neph Sy
>without also subtracting stuff you need would be more complicated. At
>.75,
>the CaO is outside normal limits anyway.
>Good luck,
>Paul Lewing, Seattle
>
>______________________________________________________________________________
>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.
_________________________________________________________________
MSN Photos is the easiest way to share and print your photos:
http://photos.msn.com/support/worldwide.aspx
Ababi on thu 13 dec 01
Cushing Satin Matt?
===================
WHITING............. 20.00 18.18%
FRIT 3134........... 25.00 22.73%
NEPHELINE SYENITE... 25.00 22.73%
EPK KAOLIN.......... 15.00 13.64%
SILICA.............. 15.00 13.64%
ZIRCOPAX............ 10.00 9.09%
========
110.00
CaO 0.75* 17.12%
MgO 0.00* 0.02%
K2O 0.03* 1.27%
Na2O 0.21* 5.32%
TiO2 0.00 0.06%
ZrO2 0.14 6.82%
Al2O3 0.28 11.73%
B2O3 0.21 5.86%
P2O5 0.00 0.04%
SiO2 2.12 51.62%
Fe2O3 0.00 0.14%
Cost/kg 2.10
Si:Al 7.47
SiB:Al 8.20
Expan 7.90
Or From his book:
V.C. SATIN WHITE LINER #420
===========================
WHITING............. 20.00 18.52%
NEPHELINE SYENITE... 20.00 18.52%
EPK KAOLIN.......... 20.00 18.52%
FLINT.............. 15.00 13.89%
ZIRCOPAX............ 8.00 7.41%
FRIT 3124........... 25.00 23.15%
========
108.00
CaO 0.79* 16.03%
MgO 0.00* 0.03%
K2O 0.04* 1.26%
Na2O 0.17* 3.87%
TiO2 0.00 0.08%
ZrO2 0.13 5.61%
Al2O3 0.42 15.38%
B2O3 0.14 3.57%
P2O5 0.00 0.05%
SiO2 2.48 53.94%
Fe2O3 0.00 0.18%
Cost/kg 1.81
Si:Al 5.95
SiB:Al 6.29
Expan 7.40
I am not sure if it helps enough for the expansion but this one for
sure is more at the matte side
Ababi Sharon
Kibbutz Shoval- Israel
Glaze addict
ababisha@shoval.org.il
http://members4.clubphoto.com/ababi306910/
http://www.milkywayceramics.com/cgallery/asharon.htm
http://www.israelceramics.org/
Judith I. Marvin on fri 14 dec 01
David - Thanks for your help. I'll be brewing up some glazes for testing
this weekend.
>From: David Hewitt
>Reply-To: Ceramic Arts Discussion List
>To: CLAYART@LSV.CERAMICS.ORG
>Subject: Re: glaze fit
>Date: Thu, 13 Dec 2001 20:30:51 +0000
>
>Judith,
>
>I would start by doing a progression blend on the silica, increasing the
>amounts in steps of 5 to 20, 25, 30 and 35 parts and see what you get.
>
>You may be interested in my article 'Calculating Crazing' which you can
>see on my web site listed under the heading Pottery Techniques.
>http://www.dhpot.demon.co.uk
>
>David
>
>In message , Judith I. Marvin writes
> >Here is a query for those glaze gurus out there. I'm really showing my
> >ignorance here. I've been trying a glaze that I just love the look of,
>i=
> >t
> >has a beautiful, buttery surface, is nice with either underglaze
>decorati=
> >on
> >or oxides brushed on top. The problem is, I'm getting crazing. Assuming
> >that what I have is poor glaze fit what should I try to improve the fit
> >without changing the look of the glaze. The clay body I'm using is
>"Idah=
> >o
> >Buff" (with grog) from Clay Art Center in Seattle. Firing cone 6
>oxidati=
> >on.
> > Here's the glaze.
> >
> > Cushing Satin Matt
> > 20% Whiting
> > 25 Frit 3134
> > 25 Neph Sy
> > 15 EPK
> > 15 Silica
> > add 10% Zircopax
> >
> >
> >
> >_________________________________________________________________
> >MSN Photos is the easiest way to share and print your photos:
> >http://photos.msn.com/support/worldwide.aspx
>
>--
>David Hewitt
>David Hewitt Pottery ,
>7 Fairfield Road, Caerleon, Newport,
>South Wales, NP18 3DQ, UK. Tel:- +44 (0) 1633 420647
>FAX:- +44 (0) 870 1617274
>Web site http://www.dhpot.demon.co.uk
>
>______________________________________________________________________________
>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.
_________________________________________________________________
MSN Photos is the easiest way to share and print your photos:
http://photos.msn.com/support/worldwide.aspx
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