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designing glazes

updated sat 7 jun 03


iandol on sun 25 may 03

Dear Wes Rolley,

A dilemma having to cope with those constraints.

You are probably right. Doing some square blend tiles would be a good =
place to start. Even line blends are useful where ash or stone glazes =
are concerned.

I am currently exploring a series of glazes using a Slate Powder that =
has come my way, courtesy of a famous Quarry. Its just the stuff =
shovelled of the ground but it must have been pounded for a hundred and =
fifty years. I am also doing some ash trials. The ash is from pruning =
residues which will not go through the mulcher.

But to design a glaze is a different prospect. It's still exploration =
but with a firm objective in mind.

First. Make a clinical assessment of what you intend to produce. =
Describe your intentions. Qualify the nature of the surface, is it to be =
glossy or dull, smooth or mat. Describe the optical qualities, is it to =
be transparent, translucent or opaque. Describe the colour. Give the =
dominant hue, the suburdinate hue, their saturation's, the tonal value.

From then on the questions are, do you wish to be empirical or use the =
glaze formulation program? If its the former I may be able to help you. =
If it is the latter, I am out in the cold, not part of my philosophy.

As far as I know only Ian Currie has published anything about designing =
and modifying glazes. He does not give recipes. And the sample you have =
admired in the book about ash glazes may be the only one which really =
showed any promise out of several hundred trials. Why not ask Phil about =

Let me know what you think.

Best regards,


Tony Hansen on mon 26 may 03

I not so sure about this.
I have been publishing websites, books for many years on
formulating glazes. My approach is the opposite, take a
native material you want to use then have it analysed.
Then use calculation software to add other materials to
it to bring its formula within typical limits for the
desired temperature. After firing and adjusting to get
the right degree of melt and surface character, do some
blending with opacifiers, colorants, variegators to produce
a range of effects. Ron Roy has promoted this approach
starting with a feldspar for many years. One good example
I use is a volcanic ash from our area, I got a glaze using
65% ash. This one is covered in the INSIGHT manual as a

Dear Wes Rolley,
As far as I know only Ian Currie has published anything about designing =
and modifying glazes. He does not give recipes. And the sample you have =
admired in the book about ash glazes may be the only one which really =
showed any promise out of several hundred trials. Why not ask Phil about =

Tony Hansen, Digitalfire Corp.

Craig Martell on wed 28 may 03


Wes wanted to know the fastest way to "design" a glaze similar to one that
Mike Dodd uses.

The best thing I can think of to tell you about that is: You probably
aren't going to do it on your lunch hour, no matter how stellar your Calc
program is. I know the glaze you are talking about. I have Phil's book
and I've seen Mike's pots in person. This is an old Bernard Leach recipe
of 40 ash 40 spar 20 clay. I've seen it in many variations and I've tried
several myself. Even if you had an analysis of Mike's raw materials you
would be out of luck because you use a different process and fire different
atmospheres and temps. You should also be aware that it's not just the
glaze that makes Mike's work so soft, lovely, and strong. It's a combo of
the clay, the slip, and the glaze itself. We must not forget Mike
either. His sense of the work and how he does things make the glaze, and
the total pot what they are.

Before we can nail a certain glaze, we must do all the laborious background
work with the myriads of materials available to us. A good glaze
calculation program doesn't know what you want. You have to know what
materials and amounts to punch into the program to get you on track. I
feel strongly that before a person can make effective use of a glaze
program you need to do all the line blends, triaxials, fusion buttons,
reading, learning, trial and error. Then the glaze programs are not so
abstract. It doesn't take a lifetime to get good results that motivate us
to continue. Some glazes, however, do not reveal themselves quickly or
easily. We have to be willing to gain knowledge and work at the
craft. Then, the discovery of what we are looking for takes on a more
profound meaning. The journey is the reward, not the destination.

regards, Craig Martell Hopewell, Oregon

Wes Rolley on wed 28 may 03

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At 11:06 AM 5/26/03 -0400, you wrote:

>My approach is the opposite, take a
>native material you want to use then have it analysed.


I have had the time to give this some thought. In the case that I cited, I=
am not sure that your approach would produce the results that I want over a=
sufficiently short time (less than my remaining lifetime).

I was starting from the view that I really loved a particular glaze in both=
its color, surface and its ability to 'break' over edges,etc. I was not=20
starting from the viewpoint of utilizing a local material. The goals are=20
different and the approach must be.

Secondly, I happen to know that that the particular glaze recipe used=20
consisted of 40$ willow wood ash (the other two ingredients are a ball clay=
and a potash feldspar), for which I have no analysis and whose local=20
substitution (ash from Canyon or Coast Live Oak) will necessarily vary from=
batch to batch but I can and do handle that.

Finally, I do not know what type of firing was done, but I can guess that=20
the pieces that I saw were reduction fired. I have only a normal electric=
firing available to me with reduction effects limited to those from=20
residual powdered charcoal in the ash...I do not wash it.

There are some other limitations in that I have always and only=20
single-fired and so need a glaze that will adhere to greenware.

"I find I have a great lot to learn =96 or unlearn. I seem to know far too=
much and this knowledge obscures the really significant facts, but I am=20
getting on." -- Charles Rennie Mackintosh

Wesley C. Rolley
17211 Quail Court
Morgan Hill, CA 95037


Wes Rolley on thu 29 may 03

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Thank you to all the glaze gurus who responded on or off line.

My intent was really to generate a discussion of the process of designing a=
glaze, and I used the Mike Dodd glaze as an example.

Craig, I know what you mean. I am not Mike, I never will be. I just would=
love to own one of those. As someone (Elca?) posted recently. There is=20
nothing more that can be taken away.

At some point, I decided to limit myself to a small set of materials (one=20
slip, 3 clays, wood ash, a feldspar, 3 oxides and a source of calcia) and=20
to try to learn completely how to control them. I still have a lot to=20
learn from this before I add too many other things to the mix, but I do=20
have a range of things that I have learned to control. I will probably=20
never have anything that looks like Dodd's glaze, and that is Ok.

What I gathered from the responses was the fact that there were as many=20
variations on the design process as there were responders, but that every=20
one made use of a glaze calculation program. One difference was when in=20
the process was it used.

Aside: I did use Insight after entering Phil Rogers analysis of Willow Ash=
into the Materials Data Base. Willow ash is so different (Almost no=20
Alumina, only 4.44% silica, but 10% P2O5) that it would be impossible to=20
approximate that using the oak ash that I have available without adding=20
other materials.


"I find I have a great lot to learn =96 or unlearn. I seem to know far too=
much and this knowledge obscures the really significant facts, but I am=20
getting on." -- Charles Rennie Mackintosh

Wesley C. Rolley
17211 Quail Court
Morgan Hill, CA 95037


Tony Hansen on fri 30 may 03

Yikes. I\'ve been reading all of these and I thought I
have the matter in hand.

The answer is neither exclusively with blending or with
analytical calculation. However I have done thousands of
tests and gone down plenty of textbook recipe blind alleys
and I really think that once you know a little about the
10 or 12 oxides you will realize that it really is simpler
understand what they do in the melt than trying to wrap your
head around the complex interactions of dozens of materials.
Understanding the chemistry level of glazes is easier
than the material level, but you do need both.
In trying to define the nirvana of formulating glazes
I could list a few things:

-Knowing about the direct relationships between
the amounts and interactions of oxides in the formula
and how these relate to the way the glaze melts and
its fired properties

-knowing about the indirect and more complex factors
governing how choice of materials affect firing and
fired properties

-knowing about factors that relate discrepancies between
glaze firing related to sourcing oxides from various

-knowing about the physical properties and mineralogy
of materials and how to select them to source the chemistry
needed while getting the desired working and application

-Being aware of the location specific factors that make
a glaze work in the hands of one person but be a failure
in the hands of the next

-Being aware of material costs, supplies and variation

-Knowing materials on the generic and name brand levels

-Knowing about material hazards

-Being keenly aware of glaze fired properties like hardness,
resistance to leaching, expansion, and how these are
related to glaze chemistry

-Understanding and recognizing the mechanisms surface
texture, matteness and gloss

-Understanding and recognizing the mechanisms of

-Understanding and recognizing the mechanisms of opacity
and various natures of opacity

-Understanding the mechanisms and nature of color

When I use the word \'mechanisms\' above I am almost always
referring to chemistry, you cannot really understanding
these things on a material level.

The \'base glaze with adjustments\' approach makes a lot of
sense to me. In theory if I have a few good base glazes
that fit my clay, fire hard and durable, and don\'t settle
in the bucket, don\'t pinhole, blister, etc. then I should
be able to add variegators, colorants and opacifiers to make
almost any glaze I like, correct?

While I often formulate glazes with the objective of
using a maxiumum of a native material, I can also visualize
what I want first. When doing this I try to define the
nature of the variegation, surface, color and opacity and
then speculate about the type of chemistry, firing
temperature, clay body base, etc that would produce this.
This is not difficult if you know the chemistry profiles
of existing matte, glossy, running, stable, crystal, etc glazes.
Adjusting an existing base make the most sense, but sometimes
you can simply write down a formula, then do a calculation to
source the oxides from the materials at hand. When I
have done this I normally get a good working glaze either
on the first try, or on the first or second adjustment.
This is not time consuming at all.
I see a fired glaze as a mixture of oxides each of
which has a \'simple personality\' and also as a mixture of
materials each of which have \'complex personalities\'.

As a cook I would not be comfortable serving a
beverage I had made from ingredients whose purpose,
source, or properties I know little about or of whose
fat, carb, chemical content I was not aware. Should
I sell ware for people to use to serve beverages in
for many years without knowing about firing glaze
properties that impact on function and safety?

Tony Hansen

Paulette Carr on fri 6 jun 03

Dear Ivor:

Since you did not answer my request directly, but rather indirectly, in your
response to Catherine, I will assume that you are working on your article, and
will let me/us know when and where it is published.

I can find information on line, biaxial and triaxial blends, but nothing on
quadraxial blending, hence, my reason for asking you to elaborate. I was
hoping that there might be a literature source from which I could learn. From
reading your posts concerning this topic, experimental design is important to
obtaining a true/good picture of what is going on with a glaze and what is
possible as a function of its components. So, if I may, I would like to ask again:
What are the high, medium and low ranges for a primary melting agent, and for
that matter how do I decide which is the primary melting agent when I have a
mixture of flux oxides?

As with Ron and John's book, I will wait (on pins and needles, of course).
If anyone does know of a source for explanation of quadraxial blending, I would
really appreciate if you would pipe in here. I do have Ian Currie's,
Stoneware Glazes, and that is my main resource for working on understanding empirical
experimental design. I use the glaze calc programs for a place to start, and
fine tune with blending experiments.

Thanks, again, for all your input of the list. Apparently, I am not the only
recipient who seeks out your comments in their daily Clayart. You are a good
teacher ... I don't understand everything that you write, but your comments
cause me to think about what you are discussing. What could be better???!!!

My best,
Paulette Carr
St. Louis, Missouri

<From: iandol
Subject: Re: Designing Glazes.

Dear Catherine White,=20

Sorry, this will not be possible. Clayart Server does not accept GIf or =
JPEG attachments.

In addition, some of this information may form part of a future article =
and I would like to keep it under wraps until publication happens.

<From: Paulette Carr
Subject: Re: Designing Glazes. The distincion between Discovery and

Good morning, Ivor!

I read your recent post/response to Wes and Stephani with interest. I am not
familiar with this matrix ("common or garden 6*6), though I am familiar with
the one that Ian Currie uses (7 x 5). Could you explain it, and send it to
me? I am continuing my ever-ongoing process of developing glazes, and have
brought myself up to speed with glaze calculation. I thought I should know
something about your approach. What are the high, medium and low ranges for a
primary melting agent, and for that matter how do I decide which is the
primary melting agent when I have a mixture of flux oxides?...