Ian Currie on sat 13 mar 99
Tom Buck wrote:
>2) Without an acceptable, reliable set of Seger Formulas for raw
>materials, the non-techie potter would be at a substantial disadvantage,
>even if a someone wrote a companion book to Lawrence's "Ceramic Science
>for The Potter" -- say, "Glaze Design ABCs".
> Locally, our sources of Pottery Materials and Equipment, keep in
>stock close to 100 materials, some high-grade chemicals, some
>raw materials slightly upgraded (clays, feldspars, minerals). In some
>cases, the dealer will obtain an analysis of some materials (clay
>composition is often uncertain). You'd have to fill in the blanks
>yourself, or revert to "grab & pitch" mixing/testing, tedious at best,
>disappointing at worst. Which camp are you in? Try to obtain/derive a
>Seger for the following materials:
>
>Albany slip or Alberta slip
.....snip....
>Wollastonite
>
>If you do this test you will see you cannot avoid some chemistry --
>nomeclature, a peek at the Periodic Table of Elements, the notion of
>hydrates, the basic structure of glass, and with time/experience you will
>not wince when you read the words "eutectic", phase diagram, triaxial
>diagram -- all part of predicting with enough precision to obtain a
>successful glaze after a few tests.
> So, Cheryl, there the project rests. I hope someone will undertake
>to write/publish the book on glaze design for non-techies; it will be a
>labour of love with little reward. As you hint, if it comes you will
>welcome it and be prepared to learn enough chemistry to become a
>successful glaze designer. Good calcs, good tests, good pots. BFN. Tom.
Hi Tom
I've recently re-subscribed to ClayArt for the third time. I usually last
a couple of weeks before I feel overwhelmed and sign off! This is not a
criticism... this is a fantastic resource, but it's practically a lifestyle
on it's own! This is my first post to this list, so in the words of
another first-timer: "Be gentle with me." :)
The method I've developed actually addresses some of the problems you've
mentioned. The original research published in my book, "Stoneware Glazes -
A Systematic Approach" admittedly is set out using Seger formula
substitutions. My new approach however does the same thing from a recipe
basis, and most of the important benefits of the original method are still
there.
Anyway the point is that the method I use actually solves a number of the
problems of unreliable materials and unreliable analyses. The "biaxial
blends" systematically vary alumina and silica over a large range for a
given set of fluxes. The results are presented in a 5 X 7 grid layout -
silica increases to the right, alumina increases to the top. If you look
at what's varying in changes in feldspars, kaolins and many other
"unreliable" materials you will find that often the main variable is
alumina and/or silica. If you are trying to reproduce a single recipe, a
switch to a new feldspar or kaolin may cause your glaze to change. With
the 5 X 7 grid you can often see where the original glaze has gone to! It
may for example have moved one glaze to the right on the grid (more silica)
and one down (less alumina). As long as you don't bump into the edges of
the experiment you can find the glaze and read off it's new recipe without
any reference to Seger formula or the analyses of materials.
This works in cases where the main variable in raw material is alumina
and/or silica. The original glaze surfaces and other characteristics are
all there, but they have moved a bit in one direction or another across the
grid.
A second point is that the systematic layout and isolation of individual
variables in the biaxial experiment sometimes allows the detection of
impurities. If you use a kaolin that has say 1% or more of iron oxide (a
common contaminant in kaolin) you will find a gradually increasing
colourant stain towards the high alumina (high kaolin) corner of the grid.
If we are unaware of this contaminant, we would read this stain as "an
effect of increasng alumina" in this set. But with more experience, and
when we see the same experiment using a high quality kaolin like Grolleg
for example, you can see the difference. And comparing an apparent
contaminant occurrence on the grid with a "Recipe Chart"* allows one to see
where it might be coming from - the fluxes, the kaolin or the silica. [* A
recipe chart is a graph picture of the grid with percentage lines of recipe
ingredients drawn over... e.g. "any glaze along this line has 40% silica in
the recipe"...30%, 20%, 10%, zero etc. And then the same for kaolin, and
then combined flux ingredients. You will see two of them on P. 50, 51 of
my book.]
Some of the effects that move around with temperature can similarly be
tracked from glaze to glaze across the grid as you fire the same set of
glazes higher and higher.
I originally evolved this recipe method (where the Seger formula is totally
unknown) for systematic variation of alumina/silica with rock glazes. (See
the book P.204-206) Although the Seger formula is not known, two of the
most effective and important variables, alumina and silica, are being
systematically varied over a wide range. Interesting things happen, and
fundamental glaze principles become obvious. [This last feature is the most
compelling advantage of this method, but in this post I'm dealing mainly
with the problems of unreliable materials and analyses.]
If your raw material has a significant variable other than alumina and
silica, it's a matter of designing an experiment that includes this
variable.
So getting back to the original point, the "non-techie potter" does not
have to be at quite the disadvantage we might imagine. There is a certain
minimum understanding necessary, but the key is the isolation of the
important variables and examining a grid of tests rather than just a single
glaze. The blind angler should fish with a net rather than a spear.
Regards
Ian Currie
L Ewing on sun 14 mar 99
Hi Tom,
I concur with Ian's approach which examines the Al2O3 =26 SiO2 variations =
around a
particular flux group of oxides. I have been using this method in my glaze =
tech
teaching programme for some years now and find it of great value at a number=
of
levels. In fact it was so useful I decided to incorporate the capacity to
design and implement such biaxial blends, along with line and triaxial =
blend, in
my Matrix Glaze Calculation Software.
http://www.tekotago.ac.nz/art/matrixgoweb/default.htm
Matrix allows these blends to be created from the recipe perspective as Ian
describes or from a Seger formula starting point. The system allows great
flexibility in designing the blends and produces all of the necessary =
printouts
to mix the full range of glazes and analyse the fired results. Blend sizes =
are
also variable. If you are not up to a full 35 sample range then you can opt=
for
something smaller.
Ian's methods have been enormously helpful not only in teaching the basics =
of
glaze theory but also in providing students with an approach for tackling =
very
common glaze problems without the need for hi tech equipment although I =
would
dispute the contention that computers are hi tech equipment these days.
Regards,
Lawrence Ewing
Senior Lecturer in Ceramics
School of Art
Otago Polytechnic
lewing=40clear.net.nz
21 Slant St
Careys Bay
Dunedin
NEW ZEALAND
ph 03 472 8801
Author of Matrix Glaze Calculation Software for Macintosh =26 Windows95
-----Original Message-----
From: Ian Currie =5BSMTP:ianc=40flexi.net.au=5D
Sent: Sunday, March 14, 1999 10:36 AM
To: CLAYART=40LSV.UKY.EDU
Subject: Glaze Design, and Tales of a Blind Angler
----------------------------Original message----------------------------
Tom Buck wrote:
=3E2) Without an acceptable, reliable set of Seger Formulas for raw
=3Ematerials, the non-techie potter would be at a substantial disadvantage,
=3Eeven if a someone wrote a companion book to Lawrence's =22Ceramic Science
=3Efor The Potter=22 -- say, =22Glaze Design ABCs=22.
=3E Locally, our sources of Pottery Materials and Equipment, keep in
=3Estock close to 100 materials, some high-grade chemicals, some
=3Eraw materials slightly upgraded (clays, feldspars, minerals). In some
=3Ecases, the dealer will obtain an analysis of some materials (clay
=3Ecomposition is often uncertain). You'd have to fill in the blanks
=3Eyourself, or revert to =22grab =26 pitch=22 mixing/testing, tedious at =
best,
=3Edisappointing at worst. Which camp are you in? Try to obtain/derive a
=3ESeger for the following materials:
=3E
=3EAlbany slip or Alberta slip
....snip....
=3EWollastonite
=3E
=3EIf you do this test you will see you cannot avoid some chemistry --
=3Enomeclature, a peek at the Periodic Table of Elements, the notion of
=3Ehydrates, the basic structure of glass, and with time/experience you will
=3Enot wince when you read the words =22eutectic=22, phase diagram, triaxial
=3Ediagram -- all part of predicting with enough precision to obtain a
=3Esuccessful glaze after a few tests.
=3E So, Cheryl, there the project rests. I hope someone will =
undertake
=3Eto write/publish the book on glaze design for non-techies=3B it will be a
=3Elabour of love with little reward. As you hint, if it comes you will
=3Ewelcome it and be prepared to learn enough chemistry to become a
=3Esuccessful glaze designer. Good calcs, good tests, good pots. BFN. Tom.
Hi Tom
I've recently re-subscribed to ClayArt for the third time. I usually last
a couple of weeks before I feel overwhelmed and sign off=21 This is not a
criticism... this is a fantastic resource, but it's practically a lifestyle
on it's own=21 This is my first post to this list, so in the words of
another first-timer: =22Be gentle with me.=22 :)
The method I've developed actually addresses some of the problems you've
mentioned. The original research published in my book, =22Stoneware Glazes =
-
A Systematic Approach=22 admittedly is set out using Seger formula
substitutions. My new approach however does the same thing from a recipe
basis, and most of the important benefits of the original method are still
there.
Anyway the point is that the method I use actually solves a number of the
problems of unreliable materials and unreliable analyses. The =22biaxial
blends=22 systematically vary alumina and silica over a large range for a
given set of fluxes. The results are presented in a 5 X 7 grid layout -
silica increases to the right, alumina increases to the top. If you look
at what's varying in changes in feldspars, kaolins and many other
=22unreliable=22 materials you will find that often the main variable is
alumina and/or silica. If you are trying to reproduce a single recipe, a
switch to a new feldspar or kaolin may cause your glaze to change. With
the 5 X 7 grid you can often see where the original glaze has gone to=21 It
may for example have moved one glaze to the right on the grid (more silica)
and one down (less alumina). As long as you don't bump into the edges of
the experiment you can find the glaze and read off it's new recipe without
any reference to Seger formula or the analyses of materials.
This works in cases where the main variable in raw material is alumina
and/or silica. The original glaze surfaces and other characteristics are
all there, but they have moved a bit in one direction or another across the
grid.
A second point is that the systematic layout and isolation of individual
variables in the biaxial experiment sometimes allows the detection of
impurities. If you use a kaolin that has say 1=25 or more of iron oxide (a
common contaminant in kaolin) you will find a gradually increasing
colourant stain towards the high alumina (high kaolin) corner of the grid.
If we are unaware of this contaminant, we would read this stain as =22an
effect of increasng alumina=22 in this set. But with more experience, and
when we see the same experiment using a high quality kaolin like Grolleg
for example, you can see the difference. And comparing an apparent
contaminant occurrence on the grid with a =22Recipe Chart=22=2A allows one =
to see
where it might be coming from - the fluxes, the kaolin or the silica. =
=5B=2A A
recipe chart is a graph picture of the grid with percentage lines of recipe
ingredients drawn over... e.g. =22any glaze along this line has 40=25 silica=
in
the recipe=22...30=25, 20=25, 10=25, zero etc. And then the same for =
kaolin, and
then combined flux ingredients. You will see two of them on P. 50, 51 of
my book.=5D
Some of the effects that move around with temperature can similarly be
tracked from glaze to glaze across the grid as you fire the same set of
glazes higher and higher.
I originally evolved this recipe method (where the Seger formula is totally
unknown) for systematic variation of alumina/silica with rock glazes. (See
the book P.204-206) Although the Seger formula is not known, two of the
most effective and important variables, alumina and silica, are being
systematically varied over a wide range. Interesting things happen, and
fundamental glaze principles become obvious. =5BThis last feature is the =
most
compelling advantage of this method, but in this post I'm dealing mainly
with the problems of unreliable materials and analyses.=5D
If your raw material has a significant variable other than alumina and
silica, it's a matter of designing an experiment that includes this
variable.
So getting back to the original point, the =22non-techie potter=22 does not
have to be at quite the disadvantage we might imagine. There is a certain
minimum understanding necessary, but the key is the isolation of the
important variables and examining a grid of tests rather than just a single
glaze. The blind angler should fish with a net rather than a spear.
Regards
Ian Currie
Tom Buck on sun 14 mar 99
Ian:
Let me first say I recognize with some awe the contribution you
have made, are making to glaze formulation.
Also, I have read most of your book but I have yet to undertake
your 5x7 spot tests approach. Mechanically, it is straight-forward but for
an old glaze-maker it is a bit too tedious. It is, however, a necessary
technique when one is using materials of dubious (or worse, unknown)
analysis. A reasonable analysis (+/-3%) of raw materials is essential for
calculating Seger Formulas and then interpreting them so as to know where
the glaze mix starts and how to do followup test tiles.
If a newbie wishes to mix his own glaze, or indeed design one from
scratch, and works at C10 R (or C10 Ox too for some), then your method
will certainly get them there in a reasonable number of runs of your 5x7
grid of 35 individual mixes. But no newbie should think the effort will be
a cakewalk; some real time and careful planning will be needed. Also, this
disciple of Currie's will get other benefits from the book, since it
provides a full explanation of many high-fire standard stoneware glaze
types (shino, copper red, tenmoku, others).
Because 1) I have chemical training, and 2) our dealers supply us
with good analyses of materials, I prefer to use the Seger Unity Formula
method, an overview of which is now available (briefly) at the Usenet
newsgroup rec.crafts.pottery. See Glaze FAQs.
Thanks, Ian, for adding to this current thread. May we meet
sometime.
Meanwhile keep well. Tom.
Tom Buck ) tel: 905-389-2339
& snailmail: 373 East 43rd St. Hamilton ON L8T 3E1 Canada
(westend Lake Ontario, province of Ontario, Canada).
Craig Martell on mon 15 mar 99
Hello Ian:
I've found the biaxial grids to be very helpful in adjusting and exploring
the variables with ash glazes. I don't get analyses of the ash I use so I
need to adjust the receipe from time to time and the biaxials are a great
aid to this.
At times, the most overlooked aspect of glaze composition is the effect and
ratio of alumina and silica. We pay great attention to flux composition and
the effect this will have on the character and color response of glazes.
When I used the biaxial receipe method to work on shino glazes, it was very
evident that alumina and silica ratios and percentages were influencing the
color response.
And as you state, the biaxials will fill in the blanks left by incorrect
analyses and materials drift. What's on paper never seems to be exactly the
same as what comes out of the ground. I think that visual examination of
glazes and fired minerals is one of the best references and indicators that
we have. Especially when compared in a systematically prepared blend.
I might also mention that this is a great time to send posts to Clayart.
Everyone is packing to head out to NCECA so those of us not going may now
dominate the list.
regards, Craig Martell in Oregon
Ian Currie on tue 16 mar 99
Some responses to Tom Buck's post dated: Sun, 14 Mar 1999 14:59:42 EST
>Ian:
> Let me first say I recognize with some awe the contribution you
>have made, are making to glaze formulation.
Thankyou Tom for the compliment. I am in awe of a simple experiment that
was first done long before my time, and which I have woven into a method.
I am also daily in awe of the knowledge displayed by contributors to
ClayArt including yourself. Can we agree to be mutually awful? :)
> Also, I have read most of your book but I have yet to undertake
>your 5x7 spot tests approach. Mechanically, it is straight-forward but for
>an old glaze-maker it is a bit too tedious. It is, however, a necessary
>technique when one is using materials of dubious (or worse, unknown)
>analysis. A reasonable analysis (+/-3%) of raw materials is essential for
>calculating Seger Formulas and then interpreting them so as to know where
>the glaze mix starts and how to do followup test tiles.
Looks as if I've given the impression this method is designed for shonky or
unreliable materials. This is just an added benefit... that it can cope
with such. The main benefit is that it reveals fundamental glaze
principles while producing some lovely glazes, and it does this very
efficiently.
> If a newbie wishes to mix his own glaze, or indeed design one from
>scratch, and works at C10 R (or C10 Ox too for some), then your method
>will certainly get them there in a reasonable number of runs of your 5x7
>grid of 35 individual mixes.
One "run" to be precise, Tom. ....assuming experimental technique is ok,
and there ARE some pitfalls that require a little care.
> Because 1) I have chemical training, and 2) our dealers supply us
>with good analyses of materials, I prefer to use the Seger Unity Formula
>method, an overview of which is now available (briefly) at the Usenet
>newsgroup rec.crafts.pottery. See Glaze FAQs.
This was how I started out, and I still use Seger formula regularly. It's
a vital tool that increases ones understanding of glazes. I'm simply
adding another. The first 35 glaze alumina/silica spread I did about 25
years ago was the most important and most cost effective experiment I've
ever done. I'm normally not a very dogmatic person but I'm willing to say
every student should do at least one! Well... every student who wants to
understand how glazes work, and I guess that's not everyone.
> Thanks, Ian, for adding to this current thread. May we meet
>sometime.
Hope so Tom. I've got some grid tiles I'd like to show you. :)
Regards
Ian
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