John Jensen on tue 19 oct 04
In an attempt to cure my crazing shino, I made a glaze with a bunch of
spodumene to lower the COE. It worked real well, except now I have a =
bit of
shivering on the rims. Except where I spritzed a bit with Soda ash =
disolved
in water...in those spots there is crazing. It seems a little soda ash =
can
make a big difference in COE...In my recipe, soda ash raises it.
John Jensen, Mudbug Pottery
John Jensen@mudbugpottery.com
http://www.toadhouse.com www://www.mudbugpottery.com
Earl Brunner on wed 20 oct 04
The soda is definitely involved, but some of the odd stuff is really most
likely the Spod. You can have shivering AND crazing on the same pot. I
would suspect that the more soluble the Spod, the more likely to be a
problem. Back in the 70's I had a great tan glaze that took iron
spectacularly, it had a lot of spod in it (and some tin). Sometimes it
shivered on a clay with iron in it if the reduction was just wrong. That
was the old grayish spod that foamed; the glaze is totally different with
the new stuff. The magic is gone.
Earl Brunner
Las Vegas, NV
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of John Jensen
Sent: Tuesday, October 19, 2004 8:22 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: glaze fault/shivering rims
In an attempt to cure my crazing shino, I made a glaze with a bunch of
spodumene to lower the COE. It worked real well, except now I have a bit of
shivering on the rims. Except where I spritzed a bit with Soda ash disolved
in water...in those spots there is crazing. It seems a little soda ash can
make a big difference in COE...In my recipe, soda ash raises it.
Ron Roy on thu 21 oct 04
Hi John,
Just to expand a little on your comments - sodium - which has the highest
expansion/contraction rate of all the oxides we use - is bound to raise the
expansion of a glaze.
Handy to know about that when you have a glaze that has a low expansion and
is causing shivering - take out some spod and replace it with spar - then
balance out the fluxes and alumina and silica.
RR
>In an attempt to cure my crazing shino, I made a glaze with a bunch of
>spodumene to lower the COE. It worked real well, except now I have a bit of
>shivering on the rims. Except where I spritzed a bit with Soda ash disolved
>in water...in those spots there is crazing. It seems a little soda ash can
>make a big difference in COE...In my recipe, soda ash raises it.
>
>John Jensen, Mudbug Pottery
>John Jensen@mudbugpottery.com
>http://www.toadhouse.com www://www.mudbugpottery.com
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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