Al Sather on wed 21 mar 01
I am relatively new potter and largely self taught. Not without some
very good mentors along the way, I must add. I am interested in
developing a simple set of quality glazes for the dinnerware I am
designing. I am also interested in some "dysfunctional" glazes for
my sculptural work.
The dilemma is that I live in the middle of the North Atlantic, and
do not have ready access to people with a sound knowledge of the
glaze technology. Thus, I am reading up on some of the glaze
analysis programs, as place to start. I also understand that if
you give a someone a hammer, you do not them make a carpenter.
However useful these programs are, I know that you need a sound
level on knowledge to read the analysis. I do not expect these programs
to make me an expert.
My two questions?
1. What recommendations can people make as to what programs
to use. I have looked at Insight, and like what it does, and attracted
to interface of Matrix. There are other programs out there, as well.
and my other question,
2. Where are good text books on glazes. I have a few general
text books, and Robin Hopper's "Ceramic Spectrum". These
are very useful starting points, but are not very technical from a
glazes chemistry point of view.
I have a science background and not afraid to dive into technical
literature. However the glaze texts I have found in the University
Library appear to be used in the engineering field are beyond my
interest and scope. Many of the glaze programs come with
extensive supporting documents, and are these sufficient?
I may add, that when I read comments from people like Ron Roy
on a glaze and run it through Insight, I can see why he says what he
says. I must admit, that looking at an analysis on my own, I am not
so adept.
Any suggestions as where to start would be helpful.
The potters In St. John's are planning a glaze workshop this summer.
St. John's Newfoundland is wonderful place to be, particularly in the
summer! If you would like to lead a week (5 days) long workshop,
I will pass your name on to the organizing committee.
Sorry this has gotten too long.
Al Sather
Dogberry Clay Studio
189 Dogberry Hill Road
Portugal Cove--St. Phillips, Newfoundland A1M 1C5
Mark & Sylvia Mondloch on wed 21 mar 01
> 1. What recommendations can people make as to what programs
> to use
After some initial frustration learning to use the program ( I think they
assume a certain level of computer savvy that I didn't have), I have found
Insight to be a good learning tool. The chemistry I found quite
straightforward and understandable. I use it on an ongoing basis whenever I
want to adjust glazes.
> 2. Where are good text books on glazes
The Potter's Dictionary by Frank and Janet Hamer is my all around 'open on
the desk- couldn't live without it book'. Unlike the name implies, it
treats subjects in an understandable but very in-depth manner.
Sylvia
Mark & Sylvia Mondloch
Silver Creek Pottery & Forge
W6725 Hwy 144
Random Lake ,Wi 53075
silvercreek@execpc.com
http://www.silvercreekpottery.com
Earl Krueger on thu 29 apr 04
On Wednesday, Apr 28, 2004, at 19:16 US/Pacific, Ivor and Olive Lewis
wrote:
> Where the concentration is lower, precipitation and crystal growth can
> happen when cooling is delayed.
> This activity may remove ingredients which we consider essential for
> the stabilisation of a Glaze. So we may be left with a glaze where the
> substance responsible for opacity, mattness, micro or macro crystal
> growth is to all intents and purposes inert but the matrix which holds
> the other things in place in the glaze is defective.
Ivor,
Another thought. As an example assume, at temperature, you have a
completely liquid melt containing, say 5% copper. Now, as that liquid
slowly cools assume 1/2 of the material crystalizes out as pure
non-copper containing substances. That leaves ALL of the copper in 1/2
as much liquid. The solution remaining would now contain 10% copper.
Essentially you have concentrated the copper in the matrix which
surrounds the crystals.
It may be that by fast cooling you create a glass containing a lower
percentage of copper which is stable whereas by slow cooling the copper
is concentrated to the point where the glass is no longer stable.
The slight difference between your view and mine is depletion versus
enhancement. In reality both would be taking place.
Earl K...
Bothell, WA, USA
Ivor and Olive Lewis on thu 29 apr 04
Dear Friends,
The recent comment of May Luk of London UK and the opinions of a senior =
member of her group, relating to the way glazes behave, should cause us =
to think more carefully about the behaviour of raw materials as they =
blend and cure in the heat of our kilns.
If materials do not dissolve to become part of the silicate fluid then =
they may remain unchanged and their individual chemistries are what they =
would have been before they were heated. If they were oxides or =
carbonates which were soluble in water, alkali or acid then they still =
retain those properties.
If substances remain in solution and contribute to a material which has =
all the properties of a true glass and that substance is, in the short =
and medium term, inert then we may have a stable glaze.
However, if chemical reactions happen at high temperature, creating =
compounds that have very high melting points, even higher than the =
maturing temperature we are using, these can start to precipitate from =
the melt if their concentration is high enough. Where the concentration =
is lower, precipitation and crystal growth can happen when cooling is =
delayed.
This activity may remove ingredients which we consider essential for the =
stabilisation of a Glaze. So we may be left with a glaze where the =
substance responsible for opacity, mattness, micro or macro crystal =
growth is to all intents and purposes inert but the matrix which holds =
the other things in place in the glaze is defective.
I think this idea may point us to a new way of designing glazes but I =
would like some discussion before going further.
Best regards,
Ivor Lewis. Redhill, South Australia
Best regards,
Ivor and Olive Lewis on fri 30 apr 04
Dear Earl,
We are both on the same wavelength here.
Your supposition will be true and your speculative result relating to
Copper ions or oxides is feasible. Testing would define working limits
for this system.
Thanks for your input.
Best regards,
Ivor Lewis. Redhill, South Australia
Earl proposed the following conclusion
> It may be that by fast cooling you create a glass containing a lower
> percentage of copper which is stable whereas by slow cooling the
copper
> is concentrated to the point where the glass is no longer stable.
> The slight difference between your view and mine is depletion versus
> enhancement. In reality both would be taking place.
David Hewitt on sat 1 may 04
Ivor,
I always read your thought provoking posts with interest. The following
paragraph is the bit that attracted me to re-read what you have said and
which seems to be the key point in your thought. Do you have an example
of such a chemical reaction which would create a compound with a very
high melting point?
In message , Ivor and Olive Lewis writes
>However, if chemical reactions happen at high temperature, creating compounds
>that have very high melting points, even higher than the maturing temperature we
>are using, these can start to precipitate from the melt if their concentration
>is high enough. Where the concentration is lower, precipitation and crystal
>growth can happen when cooling is delayed.
>This activity may remove ingredients which we consider essential for the
>stabilisation of a Glaze. So we may be left with a glaze where the substance
>responsible for opacity, mattness, micro or macro crystal growth is to all
>intents and purposes inert but the matrix which holds the other things in place
>in the glaze is defective.
>I think this idea may point us to a new way of designing glazes but I would like
>some discussion before going further.
>Best regards,
>Ivor Lewis. Redhill, South Australia
>Best regards,
--
David Hewitt
David Hewitt Pottery
South Wales UK
Web:- http://www.dhpot.demon.co.uk
Ivor and Olive Lewis on sun 2 may 04
Dear David,
In the Ca0-Al2O3-SiO2 system Wollastonite is the obvious one. The
solid state reaction between Calcium Oxide and Silicon Dioxide starts
in the region of 1000=BA C. Wollastonite has a melting point given on
the Phase diagram of 1544=BA C. Given that most glazes contain some
Calcium in one form or another it seems to be the candidate for
getting good Translucent Satin Mat finishes.
Solid state reactions are fairly common. Most of those I know come
from metallic systems. If it were not for solid state reactions we
would be unable to repeatedly harden and temper steel.
Thanks for asking. I am sure we could find other ceramic examples.
Best regards,
Ivor Lewis. Redhill, South Australia
David Hewitt on tue 4 may 04
Ivor,
Now I see that you are looking at the phase equilibrium diagram for CaO-
Al2O3-SiO2 I would agree that you could well get a psuedo-wollastonite
crystalline phase forming. You can also get other crystalline phases
forming, according to this diagram and according to the composition
point that your recipe represents on the diagram. Many of these points
might well be above your firing temperature and so I would think that
crystallisation may develop as you postulate. This, I would have
thought, would be quite a common situation. Is this how you see it?
Whether or not this produces a glaze which is *defective* depends, I
suppose, on what you want and what it is used for.
When you suggest the point you raise could point to a new way of
designing glazes, are you thinking of the use of phase equilibrium
diagrams or did you have something else in mind?
Regards,
David
In message , Ivor and Olive Lewis writes
>Dear David,
>In the Ca0-Al2O3-SiO2 system Wollastonite is the obvious one. The
>solid state reaction between Calcium Oxide and Silicon Dioxide starts
>in the region of 1000º C. Wollastonite has a melting point given on
>the Phase diagram of 1544º C. Given that most glazes contain some
>Calcium in one form or another it seems to be the candidate for
>getting good Translucent Satin Mat finishes.
>Solid state reactions are fairly common. Most of those I know come
>from metallic systems. If it were not for solid state reactions we
>would be unable to repeatedly harden and temper steel.
>Thanks for asking. I am sure we could find other ceramic examples.
>Best regards,
>Ivor Lewis. Redhill, South Australia
--
David Hewitt
David Hewitt Pottery
South Wales UK
Web:- http://www.dhpot.demon.co.uk
Ivor and Olive Lewis on thu 6 may 04
Dear David,
You are right, I am beginning to think about glaze as a two part
conundrum. The essential parts are, secondly the decorative aspects
and primarily, the need for a stable vehicle which will act as a
mechanical carrier for the other components. This is a great advantage
in solving some of the problems which beset us and can assist in
seeing why there are some anomalies which are difficult to cope with.
Yes, I use Phase Diagrams a lot, but only as thinking aids.
Pseudowollastonite is formed as the melt cools and although I have not
confirmed the fact, I think is may be just a different crystalline
form of CaSiO3. I always remember that most of the phase diagrams that
are important to us are devised by considering compositions which are
brought into a fully homogenous molten condition and then cooled to
give mixtures of minerals in varying crystalline conditions.
Differential thermal analysis helps to determine the change in state
from liquid to solid, Petrology and Analysis helps to identify and
quantify the compounds which are formed.
By the way, Huchinson -Cuff (p50) confirms the Calcia Silica Reaction
in conditions of Metamorphism. Were it a liquid reaction, then it
would be classified as an Igneous Mineral, not a Metamorphic mineral.
Now, how much more could we learn by reading about the Chemistry of
Metamorphism that might be applied to our search for good Clay Bodies
and unusual attractive glazes?
----- Original Message -----
From: "David Hewitt"
To:
Sent: Wednesday, 5 May 2004 3:31
Subject: Re: Glaze Chemistry
> Ivor,
>
> Now I see that you are looking at the phase equilibrium diagram for
CaO-
> Al2O3-SiO2 I would agree that you could well get a
psuedo-wollastonite
> crystalline phase forming. You can also get other crystalline phases
> forming, according to this diagram and according to the composition
> point that your recipe represents on the diagram. Many of these
points
> might well be above your firing temperature and so I would think
that
> crystallisation may develop as you postulate. This, I would have
> thought, would be quite a common situation. Is this how you see it?
>
> Whether or not this produces a glaze which is *defective* depends, I
> suppose, on what you want and what it is used for.
>
> When you suggest the point you raise could point to a new way of
> designing glazes, are you thinking of the use of phase equilibrium
> diagrams or did you have something else in mind?
>
> Regards,
>
> David
> In message , Ivor and Olive Lewis writes
> >Dear David,
> >In the Ca0-Al2O3-SiO2 system Wollastonite is the obvious one. The
> >solid state reaction between Calcium Oxide and Silicon Dioxide
starts
> >in the region of 1000=BA C. Wollastonite has a melting point given on
> >the Phase diagram of 1544=BA C. Given that most glazes contain some
> >Calcium in one form or another it seems to be the candidate for
> >getting good Translucent Satin Mat finishes.
> >Solid state reactions are fairly common. Most of those I know come
> >from metallic systems. If it were not for solid state reactions we
> >would be unable to repeatedly harden and temper steel.
> >Thanks for asking. I am sure we could find other ceramic examples.
> >Best regards,
> >Ivor Lewis. Redhill, South Australia
>
> --
> David Hewitt
> David Hewitt Pottery
> South Wales UK
> Web:- http://www.dhpot.demon.co.uk
>
>
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