John Sankey on sat 14 apr 07
What is it about a glaze that gives it a porous lava texture?
For example,
feldspar Custer 44%
Whiting 21
Edgar plastic kaolin 12
flint 12
titanium dioxide 11
has a large amount of titania and a CTE of 8.76, otherwise it
doesn't seem remarkable. It looks gorgeous fired at ^6!
John Hesselberth on mon 16 apr 07
On Apr 14, 2007, at 12:29 AM, John Sankey wrote:
> What is it about a glaze that gives it a porous lava texture?
> For example,
> feldspar Custer 44%
> Whiting 21
> Edgar plastic kaolin 12
> flint 12
> titanium dioxide 11
> has a large amount of titania and a CTE of 8.76, otherwise it
> doesn't seem remarkable. It looks gorgeous fired at ^6!
>
Hi John,
This is not a cone 6 glaze. It is probably a cone 10 glaze. So it is
still melting at 6. Nearly all glazes go through a period of
significant gas evolution before they are fully melted. In this case
it might well be the whiting giving off its CO2, but it could be some
impurity decomposing also. Fire it to cone 10, where it will be
mature, and you will probably find the lava texture is gone.
Regards,
John
Ron Roy on mon 16 apr 07
Hi John,
You said - at the end of your paragraph - gorgeous at cone 6 - you mean at
cone 10 - right?
The answer is - there is not enough flux to melt that glaze at cone 6 - so
it is going through the stages but never got there. You will have a
difficult time melting any cone 6 glazes with out the help of boron and or
zinc.
RR
>What is it about a glaze that gives it a porous lava texture?
>For example,
>feldspar Custer 44%
>Whiting 21
>Edgar plastic kaolin 12
>flint 12
>titanium dioxide 11
>has a large amount of titania and a CTE of 8.76, otherwise it
>doesn't seem remarkable. It looks gorgeous fired at ^6!
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
May Luk on mon 16 apr 07
Hello Ron;
With what criteria would you choose boron over zinc,
or vice versa, for more fluxing power in a glaze
formula?
Many thanks
May
[...]The answer is - there is not enough flux to melt
that glaze at cone 6 - so it is going through the
stages but never got there. You will have a difficult
time melting any cone 6 glazes with out the help of
boron and or zinc.
RR
Ron Roy on wed 18 apr 07
Hi May,
There are limitations with Zinc - the way it reacts with iron and it can
lead to pin holing because it is so sensitive to any reduction.
I favor boron because it is more "universal."
RR
>Hello Ron;
>
>With what criteria would you choose boron over zinc,
>or vice versa, for more fluxing power in a glaze
>formula?
>
>Many thanks
>May
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
John Sankey on thu 19 apr 07
The photo and recipe was given in "My Way with Clay", Rick
Malmgren, in Ceramics Monthly. (Sorry, I don't have the date,
just a photocopy of the recipe and photo.) And, yes, he says
clearly ^6, both in the recipe and the photo title. The photo
states reduction but the recipe says oxidation or reduction.
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