Daraburn@AOL.COM on fri 6 may 05
Just took out a test piece of "Lime Green" that I got on Don Goodrich's glaze
pages. I love it...a nice satin matte, not lime but a rich olive green.
However it is crazing...story of my life. Glaze calc folks, is it "fixable?" I
put it in Insight and it is within limits except for magnesium. Any
suggestions or should I just trash it? I make functional pieces and need my glazes to
be stable, durable and safe.
Dawn in Tennessee
Lime Green cone 6 ox.
Nephy Sy 45
Gerstley Borate 13
Dolomite 7
Talc 15
EPK 5
Flint 20
Nickel Oxide 2
Marc Hudson on fri 6 may 05
Hi Dawn in Tennessee,
You will need to provide more information about the clay body you are usi=
ng=20
and whether you are firing oxidation or reduction. Glazes are not "one s=
ize=20
fits all". Contact your clay supplier and get the expansion data of the =
clay=20
you are using. =20
Marc Hudson
Playing with Fire
Espa=F1ola, NM, USA
www.artfulnm.org/hudson.html
---------- Original Message -----------
From: Daraburn@aol.com
To: CLAYART@LSV.CERAMICS.ORG
Sent: Fri, 6 May 2005 15:23:37 EDT
Subject: lime green glaze help
> Just took out a test piece of "Lime Green" that I got on Don=20
> Goodrich's glaze pages. I love it...a nice satin matte, not lime=20
> but a rich olive green. However it is crazing...story of my life. =20
> Glaze calc folks, is it "fixable?" I put it in Insight and it is=20
> within limits except for magnesium. Any suggestions or should I=20
> just trash it? I make functional pieces and need my glazes to be=20
> stable, durable and safe.
>=20
> Dawn in Tennessee
>=20
> Lime Green cone 6 ox.
> Nephy Sy 45
> Gerstley Borate 13
> Dolomite 7
> Talc 15
> EPK 5
> Flint 20
> Nickel Oxide 2
>=20
>=20
_________________________________________________________________________=
_____
> Send postings to clayart@lsv.ceramics.org
>=20
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>=20
> Moderator of the list is Mel Jacobson who may be reached at=20
melpots@pclink.com.
------- End of Original Message -------
Craig Martell on fri 6 may 05
Hello Dawn:
Well, you are certainly correct about the magnesia. It's a bit high. Not
a big deal in some respects and a large part of the satin matt quality of
the glaze is due to the MgO content. The magnesia is probably causing a
large part of the crazing problem due to it's ability to form
crystals. Crystalline silica has a higher coefficient of expansion than
fused silica and this is a crysalline matt glaze. Although Magnesia can
lower the calculated expansion of glazes the formation of the crystals
negates this effect and the glaze crazes. You might want to run some
blends of this glaze and lower the magnesia. There's also some Neph Sy in
the glaze which will raise the COE and you will probably need to address
that situation too. This is a tricky one to balance but not impossible.
Hopefully you are using a well formualted, balanced claybody. It's always
good to keep in mind that glaze fit is relative to both clay and glaze.
regards, Craig Martell Hopewell, Oregon
John Hesselberth on fri 6 may 05
On Friday, May 6, 2005, at 07:05 PM, Marc Hudson wrote:
>> However it is crazing...story of my life.
>> Glaze calc folks, is it "fixable?" I put it in Insight and it is
>> within limits except for magnesium. Any suggestions or should I
>> just trash it? I make functional pieces and need my glazes to be
>> stable, durable and safe.
>>
>> Dawn in Tennessee
Hi Dawn,
This glaze should be useable. First being out of "limits" in magnesium
has little if anything to do with durability. The magnesium is high,
but if you are not running into crawling defects it is probably OK.
Since magnesium is already pretty high, I would add clay and silica to
the recipe in a proportion that keeps the Si/Al ratio the same. For
example if you took EPK up to 15 and silica up to 33 (giving a total of
128--you can renormalize it to 100 if you wish). That would lower the
expansion coefficient quite a bit. Then run a line blend with the
original and see where/if the crazing goes away. By the way your
numbers may look different than mine--it depends on which analysis you
used for Gerstley Borate--they differ quite a bit.
Regards,
John
Ron Roy on mon 9 may 05
Hi Dawn,
Recipe totals 105 without the Nickel by the way - is that correct?
You will need to have that glaze tested to see if it leaches - nickel has
some toxicity concerns by the way - avoid firing fumes and dust.
You can lower the expansion rate of this glaze significantly by subbing in
10 Spodumene for 10 Neph Sy.
You can get the same result by lowering the Neph Sy by 10 and adding 2
Lithium Carb - add a bit of talc to get the MgO back up - then adjust the
alumina by raising the EPK and then adjust the silica.
The spodumene fix would be better.
Let me know if you need more on this.
RR
>Just took out a test piece of "Lime Green" that I got on Don Goodrich's glaze
>pages. I love it...a nice satin matte, not lime but a rich olive green.
>However it is crazing...story of my life. Glaze calc folks, is it
>"fixable?" I
>put it in Insight and it is within limits except for magnesium. Any
>suggestions or should I just trash it? I make functional pieces and need
>my glazes to
>be stable, durable and safe.
>
>Dawn in Tennessee
>
>Lime Green cone 6 ox.
>Nephy Sy 45
>Gerstley Borate 13
>Dolomite 7
>Talc 15
>EPK 5
>Flint 20
>Nickel Oxide 2
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
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