karen gringhuis on thu 8 feb 07
Lili -
>To simple minds eutectics seem magical--i.e. I think
them so-- but I wonder how much use they are to
potters.<
Very useful in that, as you say, they can make magical
things happen. Or just the opposite. How useful is a
broader understanding of them to potters? Different
qn.
As Hamer says "the fact that this sort of reaction can
occur can throw some light on otherwise inexplicable
behavior in a glaze." Hear loud and clear his point of
"very difficult to establish." He means it. There are
books and books filled with data tables on possible
ingredient combinations.
>Can one actually say more?<
Not really. You've pretty well got it. A lot of
technical info well understood is indeed very useful
to potters but IMHO, detailed knowledge of eutectics
is not.
Karen Gringhuis
KG Pottery
Box 607 Alfred NY 14802
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Ivor and Olive Lewis on sat 10 feb 07
Dear Clayart Friends,
Perhaps it would help those who are forming an interest in this topic to =
have a wider view of things.
In searching for material about this topic I received the following =
reply from Bill Opperman of OSU* recently. This gives me a chance to =
acknowledge his help.
<in our library collections or the University Archives (In fact, we have =
none of his material in the archives.) He was the chair of the =
Mineralogy Department here at Ohio State University from 1913-1952. We =
have considered the publications that looked like they might be on the =
same topic but have no go candidates for your search.>> Prof. W.J. =
McCaughey drew a distinction between what happens when a melt is cooled =
and what happens when a mixed powder is heated. With the passage of time =
this distinction has been lost or disregarded, though it emerges in the =
writing of Hutchinson Cuff.
Below is a summary of some of many statements that have been published =
in recent years.
I hope some of you find them interesting !
Eutectics in Ceramic Systems.
Some definitions and opinions
"eutectic mixture A solid solution of two or more substances having the =
lowest freezing point of all possible mixtures of the components"
E,B Urarvov, Alan Isaacs. "The Penguin Dictionary of Science" Page 124, =
6 th Edition 1986.
"eutectic point Two or more substances capable of forming a solid =
solution with each having the property of lowering each other=92s =
freezing point ; the minimum freezing point attainable, corresponding to =
the eutectic mixture is the is the eutectic point."=20
E,B Urarvov, Alan Isaacs. "The Penguin Dictionary of Science" Page 124, =
6 th Edition 1986.
"The point at which the greatest degree of melt occurs is known as the =
eutectic point" E. Cooper and D. Royle, "Glazes for the Studio Potter". =
Page 18. 1978
"When a second component is added to a pure material, the freezing point =
is often lowered"
Kingery et al. " Introduction to Ceramics". Page 284. 1976
"The eutectic temperature is the temperature at which the liquidus =
curves intersect and is the lowest temperature at which liquid occurs"
Kingery et al. Page 284
"The eutectic composition is the composition of the liquid at this =
temperature, the liquid coexisting with two solid phases"
Kingery et al.
"....a mixture containing 5.5% alumina and 94.5% Silica melts at 1,549 =
deg C. This is the lowest combination of the two compounds, and is =
called an eutectic composition. The melting point of this mixture is =
called the eutectic temperature...."
Exford Newcomb, Jr, "Ceramic Whitewares. History, technology and =
Application. Page 37. 1947
"In order to attain the maximum effect, eutectic mixtures must be =
reduced to a homogeneous mass. Mere mixing of the raw materials even =
though they are finely ground together for a long time will not give the =
necessary molecular dispersion obtained by fusion"
C. W. Parmellee. "Ceramic Glazes". Page 92, 1 St Edition 1948.
"When two or more materials are mixed together it is found that there is =
one mixture which melts at a lower temperature than any other. This is =
called the "eutectic=92 mixture (Greek: t=EBctos, molten).
M. Cardew, " Pioneer Pottery" . Footnote p 50, Reprint 1977.
"The proportion of two oxides which has the lowest melting point is =
called the eutectic."
D. Rhodes. "Clay and Glazes for the Potter" Page 162, 2 Nd Edition, =
Reprint 1979
" A eutectic is the lowest melting point of two or more materials when =
blended together"
G. Daly. "Glazes and Glazing Techniques" Page 9 , 1995
"...certain elements, such for example as magnesium and silica, combine =
in definite proportions as the first opportunity in a rising =
temperature. Such a combination is called a eutectic, and only what is =
left over will harden or soften the glaze."
B. Leach, "A Potter=92s Book". 2 Nd Edition 1945, reprint, 1967.
"At the eutectic temperature both minerals crystallise simultaneously =
until all the magma has disappeared"
Y. Hutchinson Cuff, "Ceramic Technology for Potter=92s and Sculptors". =
Page 28-9, 1996
=91A eutectic composition is the particular combination of two or more =
materials in a simple system that melts at the lowest possible =
temperature of a mixture of those materials."
Y. Hutchinson Cuff. Page 265, 1996
"EUTECTIC POINT: The point at which two or more materials together melt =
lower than either one separately."
Susan Peterson. "The Craft and Art of Clay" P 380, 1992
"EUTECTIC POINT: That mixture of two or more substances which has the =
lowest melting point of the whole series".
Robert Fournier, "Illustrated Dictionary of Practical Pottery". Page 79, =
1977
"Eutectic: A eutectic represents an invariant (unique temperature, =
pressure . composition) point for a system at which the phase reactions =
on the addition or removal of heat resulting and increase of decrease, =
respectively. Of the proportion of liquid to solid phases."
E. M. Levine et al. "Phase Diagrams for Ceramists" Page 6, 1964
"Eutectic mixture. The proportional mixture of two or more substances =
which melts at the lowest possible temperature. This temperature is =
called the eutectic point."
F. Hamer. "The Potter=92s Dictionary of Materials and Techniques" Page =
114, 1975
"The first is the eutectic reaction in which a liquid becomes saturated =
with respect to the end members such that at the eutectic temperature =
two solids precipitate out of the liquid simultaneously."
M. Barsoum. "Fundamentals of Ceramics". Page 276, 1997
"....and will, therefore, contain some calcium, which is prone to form a =
wide range of eutectic melts with many materials that are generally =
quite fluid."
De Boos et al. "Handbook for Australian Potters" Page 9, 1984
"eutectic mixture A solid solution consisting of two or more substances =
and having the lowest freezing point of any possible mixture of these =
components. The minimum freezing point for a set of components is called =
the eutectic point."
Oxford concise Science Dictionary. Page 226, 3 rd Edition, 1996
"The eutectic is a mixture and not a chemical compound, although often =
(for example, in eutectics formed from one metal in another the =
crystals of solute and solvent are so fine grained, that the two =
constituents can be seen only with the aid of a powerful microscope."=20
P. J. Durrant. "General and Inorganic Chemistry" Page 159, 2.Nd Edition =
1952
"The formation of eutectics (i.e. mixtures which have a fusion =
temperature lower than that of any of their constituents), gradually =
take place and with the development of a liquid phase, the more =
refractory particles are surrounded and taken into solution in the =
liquid phase."
Harry Fraser. "Glazes for the Craft Potter". Page 13, 1998 (First =
published 1973)
"eutectic. The lowest melting point of the mixture of materials compose =
a glaze. This is always lower than the melting points of the individual =
materials."
Glen C. Nelson "Ceramics, a potter=92s handbook" Page 201, 3 rd Edition =
1971
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