Lili Krakowski on fri 9 mar 07
Alyssa. Oh dear.
Ok.
You sent in a recipe sans explanation of what temp and what firing
technique.
Recipe is:
EPK Kaolin 10
Fusion Frit 38 32
Whiting 14
Neph Sy 26
Flint 24
For which the formula is:
Na2O .221
K2O .042
MgO .006
CaO .566
SrO .165
Al2O3 .348
B2O3 . 220
SiO2 3.176
My guess it it is a c.6 glaze, and another guess is that you fire
electrically, i.e. NOT in reduction.
Now I would call that glaze a calcium/borate glaze, not a feldspathic one.
This is not because I am arbitrary but because there is a lot of calcium and
a good amount of boron in the glaze. Calcium and strontium used to be
considered "like that" (display crossed fingers)...that is before Robin
Hopper steered us down the strontium barium road. Which--I think it was Mr
Slatin--said the Russians had been on a log time. Parmelee talks about
the replacement of calcium by strontium adding a little fluidity, raising
thermal expansion, and lowering the melting point a bit...
I would, in this glaze, think of the strontium as not doing a whole lot.
And the COE is 74+ so the crazing does not astound.
Now on to something else. A dress that looked great on Julia Roberts looks
like *&*^&^% on me. Why you ask? Is life that unfair? Yes, it is.
Something that works perfectly on one body, does not on another. A
porcelain body (about which I know very little) and a casting body (about
which I know less) have stuff in them besides just clay. That "stuff" can
and will affect glaze fit. So you should not be astounded if what fits the
throwing body, does badly on the cast stuff.
Onward. The new glaze you have has zinc in it. And your mason stain turns
yukky. "Yukky" is a word of art--as the lawyers say--for yukky. (Why they
make the big bucks.) But if you read what Mason says (yes, in the catalogs)
about their greens, MOST contain chrome. And if, again, you read the Mason
page in your catalogs there is a warning on the greens (I do not know if all
of them) the caution Number 8. NO ZINC. If the stain you are using is Sage
Grey (#6500) it is Chrome, Cobalt, Silicon Dioxide, and Nickel. There is
no #8 warning. I still would try it in a Zinc free environment.
Now. I would go looking for a calcium borate glaze that is in the ball
park. And, look, right here, is recipe.
It is Mope II derived from a Cowles glaze named Mope I (which contained some
lithium)
Frit 3134 52.4
EPK Kaolin 38.1
Flint 9.5
Or
Na2O .308
K2O .006
MgO .004
CaO .683.
Al2O3 .493
B2O3 .612
SiO2 2.983
And COE 72.86
You can try it with your stains and see what happens. If it crazes, I would
just add flint .5 at a time. I use Mope II opacified. I use titanium and
or tin, but try Zircopax, as unlike t'n't it does not affect color.
As to glaze calculation. If you look under my name on Google the first
listing is the Basic Internet Glaze Course. And you can contact me off
list, if I can help.
Lili Krakowski
Be of good courage
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