Lily Krakowski on sat 14 jun 03
A request the other day asked how to/if one could convert a specific c.10
recipe to c. 6
Since fuel prices went up some 15 years ago, this question has been asked as
frequently as “Do you love me?” While the answer to the latter may be YES,
the answer to the former is an immutable, inevitable, constant NO.
It cannot be done. Cone ten is 2372oF and c 6 is 2192o F as melting points.
While this is only about 200oF it still is a respectable amount.
The hope “closest” to fulfillment would be that an extremely border-line
runny c.10 transparent, might, just might, be a stony, “under-fired matt”
at c.6.
Clay and glaze formulations are like those folk dances—I think called Line
Dances-- where a long line of dancers moves in and out, dancing up and down
the line with different partners. So the lithium steps out and the soda
steps in and the soda steps out and the potash steps in. Then calcium and
magnesium, strontium, and zinc all step in and some step out. Without
wishing to overwork the simile, alumina, boron, and silica might be thought
of as the dance callers, or organizers.
Ok.
The recipe that was asked about:
Cornwall 60
EPK 20
Dolomite 20
Whose formula is:
Potash .082
Magnesium .348
Calcium .449
Alumina .565
Silica 2.961
What could one do to convert ? For one thing as Cornwall Stone has a
higher melting point than Neph Sy—1200oC vs 1140-1200oC one could replace
Cornwall Stone with Neph Sy. And seeing how magnesium has a higher melting
point that whiting one could replace the dolomite with whiting. As this all
may not do the trick one could add some lithium to the mix. Or add some
boral frit….
Here one kisses spouse and children goodbye, packs a hamper, and goes to the
studio to do tests. Lots and lots of tests. After a week one returns home,
exhausted, rather aromatic, out of sorts, with three test tiles that show
potential.
The next day, concerned Spouse insists one stay in bed with cold
compresses on one’s forehead, and loyal family dog at one’s feet, unplugs
the phone, disconnects the doorbell, and tells the children to be very very
quiet. Why?
Because during a sleepless night one has realized that there are already
formulated c.6 recipes close enough to what one is concocting to indicate
that others have been there before.
One cracks the books, and finds in one of Cooper’s this c.6 recipe:
Shapiro Sung Yellow
Cornwall 73
Whiting 16
Neph. Sy 4
GB 7
As the recipe calls for 4 Vanadium Oxide (to make it yellow) the colorant
free glaze may be a bit too runny—something reducing the GB should help.
Formula:
Soda .184
Potash .102
Magnesium .024
Calcium .690
Alumina .415
Boron .095
Silica 3.128
Ok. Here there is a lot of the original Cornwall, but very little
magnesium.
Here is a Sarah Bodine Randy Red, listed here without the 15% Fe203
Flint 30
Kaolin 5
Soda Spar 20
Talc 14
GB 31
And the formula is
Soda .126
Potash .038
Magnesium .351
Calcium .485
Alumina .257
Boron .385
Silica 3.276
Well here there is soda which was not in the original and the KNao total is
.164, about twice what the potash was in the original.
The magnesium to calcium contents are remarkably to that of the c.10. There
is boron replacing some alumina, and more silica than in the original. Could
it just be that, once upon a time, this was that c.10 glaze, and someone
“converted “ it to c.6?
I could go on quite a while searching through note books and books but I
won’t.
The point is that there are many glazes at c. 6 that can and do look a lot
like c.10 glazes! And, truth to tell, there are many c.10 glazes that can
and do look a lot like c.6. Not ALL but plenty.
No matter what one does and how much time and trouble one puts in it is not
worthwhile—exactly BECAUSE of the materials involved.
And having used so many words to explain all this, I end with Ceil Gross’
Pumpernickel story.
A peasant found a strange looking dog wandering in his snow-covered potato
field. He caught it and brought it home. “Wife,” he said to his wife,”
this is such a strange dog, I must take it to the Czar!”
They wrap the dog in a blanket and put it to sleep between them by the
hearth, and the next morning the peasant harnesses the pony to his cart,
wraps the dog in his own coat, and heads for Moscow.
Gets to the palace and the Guards greet him with joy! He has found the
Czar’s pet Borzoi! The peasant is assured the Czar will want to see him in
person, so he is taken to the kitchen and fed a meal. Later on the Czar
sends for him. “Serf, “ says the Czar, “I cannot thank you enough-—name
your own reward!” The peasant answers without hesitation. “Your Majesty,
your Guards took me to the kitchen where I ate the most wonderful bread
imaginable. May I have the recipe so my wife can make it?” The Czar is
astounded by the man’s modesty, but the recipe is procured, and the peasant
goes home. He tells his wife she must try the recipe, and she promises she
will.
Next breadmaking day she presents him with a loaf of dark brown bread. “What
is this?” asks the peasant. “It looks and smells just like your regular
pumpernickel.” “This is bread made from your recipe.”
The peasant breaks open the loaf and tastes it. “This tastes nothing like
what they gave me….Let us go over every detail…” “Sure,” says the wife.
“Look. Here it says ‘take two pounds of the finest white flour. How is a
poor woman like me to get fine white flour? So I used my regular rye flour.
‘Knead in a pound of butter.’ Ok. Where is a poor woman like me to get
fresh butter in the middle of winter? But I had lard, so I used lard.
‘Beat in 4 eggs.’ Eggs? Maybe they have wonder chicken in Moscow but there
the hens don’t lay in winter….”
And the result: PUMPERNICKEL.
PS The above calculations would have taken me at least an hour to do with a
calculator (because I also played around with several others, which were too
far out of the ball park.) With Glaze Master it took me MINUTES.
And blahblah blah, no kinship, friendship, commercial interest--I have never
even SEEN JohnH.
Lili Krakowski
P.O. Box #1
Constableville, N.Y.
Marcia Selsor on sun 15 jun 03
Dear Lily,
Before the age of computer programs for calcultaing such things, the
rule for conversion was simply "change the feldspar to Neph. Syn. and
add 10% Colemanite which would then have cjanged to Gerstley Borate and
now would be Frit 3134 or a Borate subsititute. I have had some luck
with this at first try and some glazes needing tweeking. I converted
many glazes to ^6 in 1980 when our program at the U moved into a new
building. The requirement to fit a glaze firing into an 8 hour work day
for an assistant was the mandate. The assistant position lasted 3 years.
The glazes and firing to cone 6 reduction lasted 20+ years. Michael
Bailey will soon have a new book out on Cone 6 reduction glazes. There
will be several of the glazes I used for 20+ years in the new book.
That old rule is a good standby for starting to tweek glazes. And they
do look like stoneware reduction glazes.
Best wishes,
Marcia
Lily Krakowski wrote:
> A request the other day asked how to/if one could convert a specific c.10
> recipe to c. 6
>
> Since fuel prices went up some 15 years ago, this question has been asked as
> frequently as "Do you love me?" While the answer to the latter may be YES,
> the answer to the former is an immutable, inevitable, constant NO.
> SNIP
> The recipe that was asked about:
>
> Cornwall 60
> EPK 20
> Dolomite 20
>
> Whose formula is:
> Potash .082
> Magnesium .348
> Calcium .449
>
> Alumina .565
> Silica 2.961
>
> What could one do to convert ? For one thing as Cornwall Stone has a
> higher melting point than Neph Sy--1200oC vs 1140-1200oC one could replace
> Cornwall Stone with Neph Sy. And seeing how magnesium has a higher melting
> point that whiting one could replace the dolomite with whiting. As this all
> may not do the trick one could add some lithium to the mix. Or add some
> boral frit....SNIP
>> Lili Krakowski
> P.O. Box #1
> Constableville, N.Y.
>
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>
--
Tuscany in 2003
http://home.attbi.com/~m.selsor/Tuscany2003.html
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