Cheryl Fisher on fri 6 jul 07
Page 264 (Appendix F) Ceramics Mastering the Craft the glaze is written
as
Ball Clay 8
Gerstley Borate 22
Nepheline Syenite 51
Titanium 2
Wollastonite 14
Zinc 3
and Copper Carbonate
glassmakers = high
clay = normal
secondary fluxes = normal
"The most significant fluxes in this glaze are calcium derived from
Wollastonite and sodium derived from nepheline syenite.
It is a fairly durable glaze. The surface is mat with a lot of visual
texture.
It's cool green color is derived from copper influenced by sodium
(derived from it's Nepheline Syenite content)."
It is listed as Cone 6
On Jul 6, 2007, at 7:07 AM, John Sankey wrote:
>
> As published, this is a watery glaze that runs almost completely
> off the pot at cone 6. Does anyone have the Zakin book in which
> it was published? Was it really for cone 6?
>
> --
> (Add 'Byrd' to the subject line of your reply to get through my spam
> filter)
Cheryl Fisher
Sarasota, Florida USA
potterytalk@verizon.net
Ron Roy on fri 13 jul 07
Not enough silica to be a stable glaze and expansion is high so it's going
to craze. Why anyone would say it's a relatively stable glaze - especially
when there is copper added - is a mystery to me.
RR
>Page 264 (Appendix F) Ceramics Mastering the Craft the glaze is written
>as
>
>Ball Clay 8
>Gerstley Borate 22
>Nepheline Syenite 51
>Titanium 2
>Wollastonite 14
>Zinc 3
>
>and Copper Carbonate
>
>glassmakers = high
>clay = normal
>secondary fluxes = normal
>
>"The most significant fluxes in this glaze are calcium derived from
>Wollastonite and sodium derived from nepheline syenite.
>It is a fairly durable glaze. The surface is mat with a lot of visual
>texture.
> It's cool green color is derived from copper influenced by sodium
>(derived from it's Nepheline Syenite content)."
>
>It is listed as Cone 6
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
John Sankey on wed 18 jul 07
>Ball Clay 8
>Gerstley Borate 22
>Nepheline Syenite 51
>Titanium 2
>Wollastonite 14
>Zinc 3
>and Copper Carbonate
This is a surprisingly sloppily written formula for someone of
the reputation of Zakin. Which 'ball clay'? There are hundreds,
and they vary considerably in their analyses. Is 'zinc' zinc
equivalent or zinc oxide? Ditto for 'titanium'
"expansion is high so it's going to craze"
My version (using EPK, zinc oxide and titanium dioxide)
stands up to the usual freezer to boiling water test when
dipped thinly. At least, I can't see any crazing even at 50x
magnification...
--
(Add 'Byrd' to the subject line of your reply to get through my spam filter)
Ivor and Olive Lewis on thu 19 jul 07
Dear John Sankey,=20
I agree with you, very sloppy to curtail the appellation of an =
ingredient but it is rife as a behaviour in ceramic writings.
However, if you carefully read Ron Roy's comment in the context of the =
content of MC6G you may understand.
Ron said "Not enough silica to be a stable glaze and expansion is high =
so it's going
to craze. Why anyone would say it's a relatively stable glaze - =
especially when there is copper added - is a mystery to me."
Compositions with high levels of Sodium ions are Hygroscopic. Freshly =
created Sodium glass surfaces are readily attacked by water, leading to =
solutions of Sodium hydroxide. Copper oxide is readily leached from the =
surface of a glaze by weak organic acids.
Perhaps your samples have escaped crazing because of your thinness of =
application. This would increase interaction between clay and glaze, =
changing composition, so reducing the differential in Expansivity.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
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