tomsawyer on wed 7 mar 01
I agree with an early post of Ron Roy's saying that we might limit =
questions to one a day. Since this is my second today, I promise I'll =
skip tomorrow. It is often said and my experience confirms the adage =
that glazes often don't travel well. I tried a cone 6 firing for the =
first time in 2 years yesterday having gleaned throught the clayart data =
base for good cone 6 glazes. I did get 2 out of about 8 that were great; =
one was suppose to come out silver that came out matt black as an =
example. My question to the glaze gurus on the listserve is that I had 4 =
commercial glaze tests in the firing they all came out the way they were =
suppose to. In my limited experience using commercial glazes they seem =
to work most of the time; obviously if they didn't work on a wide =
variety of firing schedules and clays, they wouldn't be terribly =
marketable. My question is why do we have this different success rate, =
if I can call it that, with commercial glazes to glazes that appear in =
books and on this listserve? Maybe this is a dumb question but I really =
am curious. Thanking all who reply in advance.
Tom Sawyer
tsawyer@cfl.rr.com
Paul Gerhold on thu 8 mar 01
Tom,
I think you answered your own question. If commercial glazes weren't
extremely tolerant they wouldn't enjoy a lot of commercial sucess. Of course
they tend to be pretty boring as a result.
Also glazes don"t travel well for some of the following reasons:
1) A lot of glazes seem to be published after testing ,if the reader is lucky
,on one or two test tiles or similar. Many glazes don"t travel well from test
tiles to pots.
2) I suspect a lot of "potters" out there don't bother with witness cones so
published glazes can be off by a cone or more.
3) If you spend much time with finicky glazes you know that chemicals can
change from bag to bag and particle size does make a difference in really
sensitive glazes.
4) Kilns are different and position even in electric kilns can make a
difference.
5) Etc. Etc. Etc. If it were easy everyone would have great glazes. By the
way has anyone else noticed the very interesting glazes that seem to be
coming out of china in huge commercial quantities. Check out pots in Pier
One, Also a year ago we were in Chinatown in San Francisco and saw huge pots
with crystal glazes for no money which the shopkeeper would reduce at the
slightest provocation. If you make your living with crystal glazes
beware.Looks to me like the computer revolution has taken the challenge out
of crystals. As a note of humor the salesperson told me in an effort to make
the pots more precious that the crystals were the result of abalone shell in
the glaze,
John Hesselberth on thu 8 mar 01
tomsawyer wrote:
My question is
>why do we have this different success rate, if I can call it that, with
>commercial glazes to glazes that appear in books and on this listserve?
>Maybe this is a dumb question but I really am curious. Thanking all who
>reply in advance.
Hi Tom,
I would speculate there are several reasons why glaze recipes don't
travel very well.
1. "Minor" substitution of ingredients. Say I don't have any EPK so I
substitute KY#4 ball clay. After all clay is clay, right? Wrong. If
you look at the composition there are really quite different. Same with
feldspar substitions. Also traded recipes are more likely to contain
variable or partially soluble ingredients like gerstley borate or lithium
carbonate. You won't see commercial glaze manufacturers using those
ingredients. They have a high focus on frits, stains and reliable clays
and feldspars.
2. Particle size differences, e.g. some people might be using 325 mesh
silica, others 200 mesh. This will cause a difference in melting rate
3. Mixing and screening differences. How well are you getting the
materials dispersed? How much water have you used? How much and what
kind of dispersing or stabilizing agents? All of these can affect how a
glaze goes onto a piece of bisqueware. Commercial manufacturers
standardize all that.
4. This one is speculation from a very limited set of observations, but I
am suspicious that commercial matte glazes are more likely to be
formulated as poorly melted mattes instead of recrystallized mattes.
Unmelted mattes are easier to reproduce that recrystallized ones because
recrystallized ones are VERY dependent on controlled cooling rate.
Unmelted ones are also very much less stable. Try putting some of your
commercial mattes in vinegar for 3 days and see what happens to
them--this will give you a good idea whether they are unmelted or
recrystallized.
So in total, the glaze manufacturers know exactly what they have done to
make the glaze and reproduce it very carefully. Traded recipes, on the
other hand, are not fully documented and people are very likely to
substitute or do things differently than the recipe developer.
Regards, John
"The life so short, the craft so long to learn." Chaucer's translation of
Hippocrates, 5th cent. B.C.
michael wendt on sat 10 mar 01
I watched to see IF anyone brought this up before I answered:
One reason not mentioned for glazes not traveling well is clay body
interaction. I have spent the last 28 years working with Helmer Kaolin to
refine the body so that it would form the way I want AND produce the desired
glaze interactions. When I sent a glaze formula to Tony C. that works
beautifully with my clay body, he informed me that it didn't fuse at all on
his clay body. We discussed body formulas and so I mixed a batch without
Nepheline Syenite. It finally became clear: Your clay body plays a vital
role in glaze development.
One key body ingredient in high fire glaze interaction is Nepheline
Syenite. The sodium probably becomes volatile and reactive enough to speed
the melt at the clay -glaze interface and cause totally different reactions
from a body made with potash feldspar. I have noticed similar volatility
with petalite bodies.
Email me if you want the experimental data.
Regards,
Michael Wendt wendtpot@lewiston.com
will edwards on sun 11 mar 01
Hello,
When I send out a glaze I sometimes hear back from the other side of the =
world
which makes me happy. But on the other hand I have to acknowledge that
materials vary from site to site. Thats why I have many different analysi=
s for
such as this. (Yes, I have British and Australian and a few other analyti=
cal
records via MATRIX tm. and harvesting from companies that post theirs on =
their
public info sites).
If Alisa would provide me with her analytical records on the chemicals I =
could
see just how close some are to what others are using and also base it aga=
inst
the originals that I write.
While I am not a user of Tony's Insight(tm) program (Will get it next rou=
nd)I
do know that the 20x5 recipe has a great record and most anyone should ga=
rner
a good start from using it with various oxides for color.
The above recipe (20x5)is one that I have stated as being easy to use and=
easy
to understand. Check his web-site out and take it from there.
Don't be fooled into thinking Frit based formulas aren't a great choice. =
Also
those with less materials are sometimes better than more materials. Frits=
often contain many varieties of chemicals in order to sustain the effect/=
melt
the company intended to sell it for. Commerical use of the materials mean=
s a
much closer chance of repeated results also since they can't afford to sc=
rew
up a mass producer they supply.
Now not to confuse you all I do have some base recipes that call for near=
ly a
dozen things. I hate the crap out of all that but it is the beast I took =
on
when I changed out GB in all my work. I have since narrowed some ways dow=
n to
fix many of them in other ways. Gerstley was a good thing at one time now=
we
have to look forward to the next level and make that change.
William Edwards
Alchemy 101
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