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tom's glaze challenge - was 're: the j&r book; what's new?'

updated tue 23 jul 02


Wanda Holmes on sun 21 jul 02

Ok, Tom, as a glaze apprentice, I'll take the challenge. Here's my
glaze recipe based on your suggested seger formula (I did use a glaze

Minspar 200 39
Nepheline syenite 26
Whiting 7.2
Zinc oxide 6.8
Silica 14

Na2O 0.29
K2O 0.11
MgO 0.00
CaO 0.30
ZnO 0.30

Al2O3 0.55

SiO2 3.53
P2O5 0.00
TiO2 0.00
Fe2O3 0.00


Expansion: 77.3

Here are my concerns about this recipe - the Al:Si ratio seems low for a
glossy glaze. That seems like a lot of Al2O3 - is it really going to
melt? With all that zinc is it going to leach badly? And, finally, I
suspect it will craze like hell. Are these valid observations? If so,
I'll take a stab at fixing them. In exchange there's something that you
glaze gurus know that still seems like black magic to me - how do you
predict the cone at which any given glaze will mature? Is it simply a
matter of comparing the formula to the various limit formulas in the
literature? Are you looking at some key ratio?? Curious minds want to


-----Original Message-----
From: Ceramic Arts Discussion List [mailto:CLAYART@LSV.CERAMICS.ORG] On
Behalf Of Tom Buck
Sent: Sunday, July 21, 2002 3:11 PM
Subject: the J&R book; what's new?

There have been some "peculiar" expressions of praise and denial
over the issuance this year by John Hesselberth and Ron Roy of their
book "Mastering Cone 6 Glaze". The odd comment hinted these gentlemen
were seeking sales to line their pockets.
Let me make clear one thing: if J&R manage to recover the costs
of producing this publication, as independent publishers, they will have
achieved something that very very seldom happens. and I know whereof I
speak ... I was, years ago, in publishing as editor/manager of an
engineering publication issued monthly. In an excellent year, we made
10% profit (before tax) on a budget of $2.5 million. There were lean
years when that ROI was close to zero. Book publishing is even more
Should you be a ceramics engineer in industry you will have
surely been fed on Parmelee/Harman and Kingbery, and hence be fully
aware of "old-hat stuff" (as one Clayarter said) covered in the J&R
book. Yet, in five years of attending NCECA conferences, the only such
persons I met were in the exhibitor booths, not those attending as
potters and teachers.
There is a real need for younger potters of today to become
glaze literate. Who, for example, can complete this request for me:
Please design for me a gloss base glaze for Cone 3. I give you a
hint: start with the Watts Formula: 0.4 KNaO; 0.3 CaO; 0.3 ZnO; 0.5/0.6
Al2O3; 3.5-3.55 AiO2. If you hand-calculate, it will take awhile; if you
do it via a glzcalc program, it will still take sometime if you do it
via interpolation, and perhaps the fastest way is a computer program
that allows you work directly from a Seger Formula to a Batch Recipe.
In the J&R book are examples of Seger Formulas, alongside Batch
Recipes. In my view, this will encourage many potters to explore further
these relationships, and lead to more potters becoming glaze literate.
It helps, too, that the examples of good glazes cited in the
book actually do produce excellent interesting glazes for functional
I await my new C3 base glaze. TIA. Peace. Tom B.

Tom Buck ) -- primary address.> "alias" or secondary address.
tel: 905-389-2339 (westend Lake Ontario, province of Ontario, Canada).
mailing address: 373 East 43rd Street, Hamilton ON L8T 3E1 Canada

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