Wyndham Dennison on tue 23 feb 10
> I use a similar recipe with 16% Zinc Oxide and it does pudding up when it
> sits. When I'm ready to use it, I beat it with a drill mixer and then add
> Darvan 7 (carefully or it will hardpan). I'd be curious to hear how the
> macro-crystalline glazers deal with zinc oxide.
Sylvia, macro crystalline glazes call for around 25% zinc oxide but most
use calcined Zinc oxide to solve these issues. These glazes also do not
use more than 1 % clay or none at all so the problem is just the
opposite, getting it to keep from dropping out. For me the solution is
Epsom salts, this will keep it in suspension.
Patty on wed 24 feb 10
My crystalline glazes have 25% zinc oxide. I use calicined Zinc oxide. I
use about.5% Veegum T in the mix and only mix glazes the day of glazing or
the day before. I use all the mixed glaze in that day or two. Never let i=
Mark and Sylvia Mondloch on wed 24 feb 10
I was under the impression that zinc oxide which has been calcined
re-hydrates when exposed to moist atmosphere or water in the glaze bucket.
Is that wrong?
Sylvia and Mark Mondloch
Silver Creek Pottery & Forge
> Sylvia, macro crystalline glazes call for around 25% zinc oxide but most
> use calcined Zinc oxide to solve these issues. These glazes also do not
> use more than 1 % clay or none at all so the problem is just the
> opposite, getting it to keep from dropping out. For me the solution is
> Epsom salts, this will keep it in suspension.
Patty on thu 25 feb 10
My first crystalline glaze workshop was with Tim Hull in Connecticut. He
used Veegum T in his cone 10 glazes. He said it had solved his settling
problems when he had to change formulas after one or more of his ingredient=
was no longer available. So I bought some to use when I was going to start
working with cone 6 crystalline glazes. It seems to work fine. So I see n=
reason to change to another gum.
William & Susan Schran User on thu 25 feb 10
On 2/24/10 11:14 PM, "Patty" wrote:
> My crystalline glazes have 25% zinc oxide. I use calicined Zinc oxide. =
> use about.5% Veegum T in the mix and only mix glazes the day of glazing o=
> the day before. I use all the mixed glaze in that day or two. Never let=
> sit around.
The problem with zinc is the high coefficient of expansion and shrinkage as
it dries on the pot. With the high percentage of zinc we use in crystalline
glazes, this can lead to all sorts of issues.
Though using calcined zinc does help help with this to a limited degree, by
using calcined zinc we can get a more accurate measurement of the actual
amount of zinc we are weighing out to add into the glaze. Uncalcined will
weigh a bit more.
The issue of long term storage of crystalline glazes is more the slightly
soluble frit 3110 or other sodium containing materials. It's tough to use a
high percentage of sodium bearing materials and keep them out of solution.
Since crystalline glazes contain virtually no clay and a very high
percentage of frit, it's tough to keep the glazes in suspension and keep
them from cracking off the pot as they dry. Our solution is to add gum
compounds. I use CMC and apply the glaze with a brush.
Patty - What was your choice to use Veegum T rather than other gums?
Are you applying glazes by spraying?
William "Bill" Schran