Ivor and Olive Lewis on wed 18 feb 04
Dear John,
I have no problems accepting Earl's Dynamic Dance Hall Model of
thermo-dynamic-kinetics. Kingery and his collaborators call it
"Thermal Diffusion". It leads to a process called "Liquid Phase
Sintering". But it can also lead to the very opposite in some
circumstances where the product or products of the union exhibit a
higher melting point than either or any of the original ingredients.
So I stick with the simpler idea that our glazes do what they do
because the substance with the lowest melting point becomes a fluid
and initiates or promotes an environment in which all of the other
ingredients may dissolve. Though, be warned, you may not know you have
included that compound.
I reckon its time you fellows, and the ladies as well, invested a few
dollars in "Introduction to Ceramics', ISBN 0-471-47860-1. Beside my
favourite Ch 10 there are some other juicy sections like "Atom
Mobility", "Reaction Between Solids", "Phase Transformations" and
"Ceramic Phase Equilibrium Diagrams." Nor should "Deformation, Viscous
Flow and Creep" be ignored. All good reading for Artists with open
minds.
In theory, the two formulae and their predicted melting points that I
gave Ababi would be good cases to show Earl's notion is true. Get
your glaze calc programs to work. Find the ideal mixtures of either K-
or Na-Felspar, Quartz and Kaolin and fire to just above 1050=BAC.
Then report back to Clayart. Tell us what your recipes were and
describe your results.
Best regards,
Ivor Lewis. Redhill, South Australia
----- Original Message -----
From: "John Hesselberth"
To:
Sent: Wednesday, 18 February 2004 6:57
Subject: Re: How Do Glazes Melt?? The First Time
> On Tuesday, February 17, 2004, at 02:11 AM, Earl Krueger wrote:
> >
> > A melt has occurred at a temperature lower than what would
> > be required to melt either A or B.
> >
> >
> > At least that's the model that works for me.
> >
> > Earl K...
> > Bothell, WA, USA
> Hi Earl,
>
> That's a model that works for me too, but I had just about let Ivor
> convince me that was all hogwash--at least that is what I think he
was
> trying to convince us of. His theory of the lowest melting material
> melting and then acting as a solvent for the other materials seems
to
> make sense -- until this flash came to me when I was perusing Hamer
and
> Hamer and I realized that some glazes are made from mixtures of
> materials that don't melt at all at glaze temperatures if, as
Michael
> says, they are in individual piles.
>
> John
> http://www.frogpondpottery.com
> http://www.masteringglazes.com
>
>
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John Hesselberth on thu 19 feb 04
Hello Ivor,
On Wednesday, February 18, 2004, at 12:38 AM, Ivor and Olive Lewis
wrote:
> Though, be warned, you may not know you have
> included that compound.
So are you suggesting that there are always enough low melting
impurities in the materials we use it initiate the 'solutioning'
process you propose?
> I reckon its time you fellows, and the ladies as well, invested a few
> dollars in "Introduction to Ceramics', ISBN 0-471-47860-1. Beside my
> favourite Ch 10 there are some other juicy sections like "Atom
> Mobility", "Reaction Between Solids", "Phase Transformations" and
> "Ceramic Phase Equilibrium Diagrams." Nor should "Deformation, Viscous
> Flow and Creep" be ignored. All good reading for Artists with open
> minds.
I've had Kingery for some time and, while it is certainly a treasure of
information, it is a bit too esoteric to really get to the nub of my
question. I want to know what those molecules are doing in plain terms.
I want to get inside those crystals and feel what is happening.
I have always found that until you can describe it that way, without
resorting to differential equations and concepts like free energy, you
don't really understand it--at least I don't. Virtually every one of
the equations in Kingery (and other similar books) have at least one
'fudge factor' (they are, of course not called that--they are called
things like diffusion coefficients and somebody's constant of one kind
or another or just plain 'constants') in them which has buried in it
all the not-understood things. I know--in my graduate thesis work I
derived some those fudge factors. It is just that I call them what
they are instead of dressing them up in a fancy name.
While Chapter 10 in Kingery helps to describe in mathematical terms
some of the things that happen as our materials melt and solidify (with
an ample supply of fudge factors), it does little to tell me what is
happening. Some people are satisfied with the mathematical
descriptions--I'm not, except in the one or two areas where I know how
to derive them first principles. Earl's description is much more to my
liking. That's also why I am tempted to buy into your solutioning
hypothesis. It is in terms that give me a feel for what is happening.
But I still have yet to understand what becomes the solvent and how it
gets from the solide to the liquid phase in the zinc base glaze I
mentioned in my earlier post--unless Earl's description is operative.
Until then I will keep wondering, but the answer in terms I want won't
come out of Kingery. I also wouldn't recommend Kingery to anyone who
doesn't have a fairly strong scientific and mathematical background.
Some grounding in thermodynamics, chemical kinetics, heat transfer,
mass transfer, differential equations, and probably a few other areas
is necessary to understand 90% of what is in that book.
Regards,
John
http://www.frogpondpottery.com
http://www.masteringglazes.com
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