SolvejgMa@aol.com on tue 11 feb 97
I hope someone can answer some questions for me, and if they''ve been asked
recently I'm sorry, my e-mail has been forwarded to the Twilight Zone for
weeks.
I'm trying to re-formulate a ^7 glaze for my porcelain clay body.
Actually, the notes say it's ^7 - 9.
Green Turquoise (ox)
Neph Sy 35.9
Whiting 20.52
Zinc Oxide 5.13
Strontium Carb 7.67
Flint 30.78
Add: Tin Oxide 5%
Copper carb 2%
I fired to a hard ^7 with a half hour "soak" at the end. (14 hours in all)
The glaze is a nice blue green gloss where thick, with pale green matt
crystals where thin. I don't mind the crystals at all, in fact they give me
ideas for decorations. The problem is the glaze crazes badly, and it's
easily scratched. I did a unity formula on it, but don't know how to
translate the results. (I'm just beginning to learn glaze calc)
Okay... I figure the crazing could be from the sodium in the Neph Sy, so if
I changed to Custer spar, would that help take care of it? And if I added
more CaO-whatever, like more whiting, would that make the surface more
scratch resistant? I'd like to keep the crystals and color, so if anyone has
any suggestions I'd really appreciate hearing them. I have lots of glaze
texts and handouts and chemical formulae scattered around, but sometimes I
feel like I'm chasing my tail!
Oh, one more.... (for now) How can I tell by a unity formula what firing
range a glaze covers? Or actually, if I have a specific cone in mind (7),
what chemical or combination do I have to solve for? Is it the Al203 or the
KNa20? If the alumina, do I figure boron into it too? (Gerstley B. gives me
a pain in my calculations.)
This is a lot, I know, but if anyone could give me just a few answers I'd
be greatful.
Thanks!
Kat in Salem, Or
Lili Krakowski on fri 14 feb 97
You don't say what the glaze is DOING wrong that it NEEDS reformulation.
If it is too fluid there are two easy roads; remove your neph.sy and
replace
with a soda spar. Or start adding clay in 5% increments. (The added
alumina will make more refractory.) If it is crazing start adding silica
in 5% increments. I learned as a student a rule of thumb: before you
finalize a glaze "load it up" with silica--see how much it will take
before it either gets too refractory or does some other bad thing, then
stay just a tiny bit below that maximum. I still like to do that. With
all this said: consider also adding like 3% bentonite to your mix. With
no clay it it at present it probably is not a whole lot of fun to use.
Lili Krakowski lkkrakow@edisto.cofc.edu
On Tue, 11 Feb 1997 SolvejgMa@aol.com wrote:
> ----------------------------Original message----------------------------
> I hope someone can answer some questions for me, and if they''ve been asked
> recently I'm sorry, my e-mail has been forwarded to the Twilight Zone for
> weeks.
>
> I'm trying to re-formulate a ^7 glaze for my porcelain clay body.
> Actually, the notes say it's ^7 - 9.
>
> Green Turquoise (ox)
>
> Neph Sy 35.9
> Whiting 20.52
> Zinc Oxide 5.1
> Strontium Carb 7.67
> Flint 30.78
>
> Add: Tin Oxide 5%
> Copper carb 2%
>
> I fired to a hard ^7 with a half hour "soak" at the end. (14 hours in all)
> The glaze is a nice blue green gloss where thick, with pale green matt
> crystals where thin. I don't mind the crystals at all, in fact they give me
> ideas for decorations. The problem is the glaze crazes badly, and it's
> easily scratched. I did a unity formula on it, but don't know how to
> translate the results. (I'm just beginning to learn glaze calc)
>
> Okay... I figure the crazing could be from the sodium in the Neph Sy, so if
> I changed to Custer spar, would that help take care of it? And if I added
> more CaO-whatever, like more whiting, would that make the surface more
> scratch resistant? I'd like to keep the crystals and color, so if anyone has
> any suggestions I'd really appreciate hearing them. I have lots of glaze
> texts and handouts and chemical formulae scattered around, but sometimes I
> feel like I'm chasing my tail!
>
> Oh, one more.... (for now) How can I tell by a unity formula what firing
> range a glaze covers? Or actually, if I have a specific cone in mind (7),
> what chemical or combination do I have to solve for? Is it the Al203 or the
> KNa20? If the alumina, do I figure boron into it too? (Gerstley B. gives me
> a pain in my calculations.)
>
> This is a lot, I know, but if anyone could give me just a few answers I'd
> be greatful.
>
> Thanks!
>
> Kat in Salem, Or
>
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