sandra m benscoter on sun 7 sep 97
On Aug. 25th Laura in Oregon posted a recipe for a ^5-6 clear glaze:
Soda Feldspar 40
Gerstley Bor. 30
Ball Clay 20
Flint 10
I used F4 as the soda feldspar and fired to ^6 both high fire porc. and a
high fire buff stoneware. The porc. has a lot of crazing and the
stoneware had some. I intend to replace the F4 with Neph. Sy. or G200.
to see if it eliminates the crazing, before I alter anything else.
I would also like to use this clear glaze on a low fire porc. and white
stoneware (^6-7).
Any suggestions? Or am I being unrealistic and should alter the recipe
for just one type of clay body?
Thanks for anyone's input. If this has been discussed before on Clayart,
please reply to my 'e' address.
Last year a friend and I took a long clothes line rope, ran it through
pulleys at both ends (like before the days of indoor dryers!) and hung
our test tiles on (like clothes drying). We called it line blending. It
made us appreciate the amount of work we put into testing glazes.
Sande
sbenscoter@juno.com
Ron Roy on tue 9 sep 97
Adding either g200 or Neph Sy will RAISE the expansion. This glaze has a
low expansion to start with - It would not craze on any of the cone 6
stoneware clay I am familar with. Are you sure it's crazing and not the
opposite?
I think you should try it with g200 and Neph Sy - the g200 is the better in
terms of a durable glaze - it's a bit short of silica with the Neph Sy.
That is a lot of Gerstley Borate to have in a glaze - I would suggest
lowering it somewhat and substituting a frit like 3124.
It is unrealistic to expect the same glaze to work at cone 6 and cone 04 -
lowering the clay pecentage would be the the first thing to try.
>----------------------------Original message----------------------------
>
>On Aug. 25th Laura in Oregon posted a recipe for a ^5-6 clear glaze:
>Soda Feldspar 40
>Gerstley Bor. 30
>Ball Clay 20
>Flint 10
>
>I used F4 as the soda feldspar and fired to ^6 both high fire porc. and a
>high fire buff stoneware. The porc. has a lot of crazing and the
>stoneware had some. I intend to replace the F4 with Neph. Sy. or G200.
>to see if it eliminates the crazing, before I alter anything else.
>I would also like to use this clear glaze on a low fire porc. and white
>stoneware (^6-7).
>Any suggestions? Or am I being unrealistic and should alter the recipe
>for just one type of clay body?
Ron Roy
Toronto, Canada
Evenings, call 416 439 2621
Fax, 416 438 7849
Studio: 416-752-7862.
Email ronroy@astral.magic.ca
Home page http://digitalfire.com/education/people/ronroy.htm
David Hewitt on tue 9 sep 97
To achieve non-crazing on porcelain can be difficult. It would seem very
worthwhile to me to try and find a porcelain which has the highest
available coefficient of expansion in order to give you the best chance.
If I take your Ball Clay as CM #4 Tennessee Ball, my glaze program gives
this as having a 3.89 x10-6 /oC linear coefficient of expansion using
English & Turner figures. That this crazes on a porcelain does not
surprise me at this figure.
A recipe which I have tested and which does not craze on Potclays 1149
porcelain, but does on Potclays 1147, is as follows:-
Wollastonite 100
China Clay 200
Potash Feldspar 100
P2960 Low Exp Frit 250
(PotteryCrafts)
Quartz 50
___
700
In message , sandra m benscoter writes
>----------------------------Original message----------------------------
>
>On Aug. 25th Laura in Oregon posted a recipe for a ^5-6 clear glaze:
>Soda Feldspar 40
>Gerstley Bor. 30
>Ball Clay 20
>Flint 10
>
>I used F4 as the soda feldspar and fired to ^6 both high fire porc. and a
>high fire buff stoneware. The porc. has a lot of crazing and the
>stoneware had some. I intend to replace the F4 with Neph. Sy. or G200.
>to see if it eliminates the crazing, before I alter anything else.
>
>I would also like to use this clear glaze on a low fire porc. and white
>stoneware (^6-7).
>
>Any suggestions? Or am I being unrealistic and should alter the recipe
>for just one type of clay body?
>
>Thanks for anyone's input. If this has been discussed before on Clayart,
>please reply to my 'e' address.
>
>Last year a friend and I took a long clothes line rope, ran it through
>pulleys at both ends (like before the days of indoor dryers!) and hung
>our test tiles on (like clothes drying). We called it line blending. It
>made us appreciate the amount of work we put into testing glazes.
>
>Sande
>
>sbenscoter@juno.com
>
--
David Hewitt
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