Ron Roy on sat 7 mar 98
Hi Jeff,
Excellent thinking - you lowered the expansion to get rid of the crazing
and got the silica up to were the glaze is now durable as well.
Now everything is OK if your body is a porcelain - if you are using this on
one of those (I am tempted to say dumb) stoneware clay bodies with
significant cristobalite in them then you had best test this glaze for fit.
Make a six inch high by three inch wide cylinder and keep the clay about
3/8 ths thick - you don't need a bottom - in fact you can make em out of
slabs. Make a bunch to test your other glazes if you want. Only glaze the
inside and fire them. If they aren't cracked when they come out of the kiln
- freeze em for 24 hours - if they aren't cracked then - fill em with
boiling water while they are still frozen. Careful now - if you happen to
be holding it when it cracks you will wish you weren't.
You can also do some with glaze inside and outside - this tends to equalize
the strain with a low expansion glaze - and remember - a low expansion
glaze on the inside and a crazing glaze on the outside is the worst of all
possible combinations.
If you want my opinion about the suitability of your clay body just email
me the recipe, cone fired to and atmosphere.
>I use the following red glaze cone 10 reduction, only it has some fit problems
>for my clay body.
>
> RED Cone 10
>
> CUSTER 752.675
> COLEMANITE 103
> WHITING 112.5
> TIN OXIDE 9.675
>ADD
> COPPER CARB. 4.5
>
>It seems very short, as in it needs some flint. I have adjusted the formula as
>follows:
>
> RED REVISED Cone 10
>
>CUSTER 752.675
>COLEMANITE 103
>WHITING 112.5
>TIN OXIDE 9.675
>FLINT 176
>
>ADD
>COPPER CARB. 4.5
>
>will this help??? all in put is greatly welcomed.
>
>trying to work things out in cold missouri.
>jeff walker
>
>jdpotter@iland.net http://www.iland.net/~jdpotter
Ron Roy
93 Pegasus trail
Scarborough Otario
Canada M1G 3N8
Phone: 416-439-2621
Fax: 416-438-7849
Web page: Home page http://digitalfire.com/education/people/ronroy.htm
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