Bill Merrill on sun 22 nov 09
It seems that the issue now on Clayart is trying to get a definative =3D
answer how eutectics work between two or more materials. The more =3D
materials there are in a mix the harder it will be to understand unless =3D
one is a ceramic engineer dealing with eutectics of materials. For =3D
example. Take a feldspar that may melt at a certain temperature and add =
=3D
small percentages of flint to the spar and the mix will melt at a lower =3D
temperature. Keep adding flint to your mix and evEntually the mix will =3D
start to siffen up and eventually be very dry due to the domination of =3D
sppar by flint since flint by itself won't melt until at least 3100 =3D
degrees F. =3D20
=3D20
It would perhaps more beneficial for individul potters to do a series =3D
of fusion buttons using each material you want to test with different =3D
feldspars. Each tile has five fusion buttons on the tile with each tile =
=3D
being composed of a feldspar mix with the materrial being tested. There =
=3D
will be a progressive melt on the tile showing the melt pattern. Also =3D
beneficial is to due single fusion buttons of all individual materials. =
=3D
Materials change, Foote Mineral Spodumene would turn orange and grow at =3D
least 2 1/2 TIMES IN SIZE AT CONE 10 IN REDUCTION. You can do this at =
=3D
any temperature range. I still have hundreds of those tests and they =3D
have been beneficial to me by seeing how they react. knowing your =3D
materials will be more very helpful to a potter. When you look at unity =
=3D
formulas for a glaze the ratio between Alumina and silica is one way to =3D
tell what surface a glaze will have. If the ratio is say, 1 to 4 the =3D
glaze will be likely a matt glaze. If it is 1 to 10 the likely hood is, =
=3D
it will be a glassy glaze. As you look at the lower temp glazes those =3D
ratios are different. If you look in Rhodes "Clay and Glazes for the =3D
Potter" there are glazes at different temperatures. The unity formulas =
=3D
are there for comparison. If you use a different feldspar to try and =3D
calculat or verify they are correct thy won't be because the feldspar =3D
Rhodes used is now longer being mine. He used different spars, but for =3D
glaze #32 he used Oxford spar.
=3D20
If you do a fusion button of Barium you will find it shrinks and =3D
produces a halo from the gases it apparently produces. Your base glazes =
=3D
need to be of a specific chemical base to encourage the develoment of =3D
certain colors. Add copper to the #32 a high alumina mat glaze and you =3D
will not get a copper red. Add copper to a glaze that is highly =3D
alkaline, like Carlton Balls cChun glaze and you will get a sang de boef =
=3D
copper red in reduction. Add copper to a spodumene/barium glaze and you =
=3D
will get a green, and so on and on.
=3D20
I used a 10 gram Coors porcelain crucible to make the fusion buttons.
=3D20
As the glazes go lower and lower in temp especially using frits the =3D
calculations become more complex on paper. I use a cone 016 Raku glaze =3D
that has 2 different frits, flint and lithium as a base. It is complex =3D
on paper, but is simple to figure out what temperature it mellts at by =3D
just simply looking at the materials in the glaze.
=3D20
The initial question was about eutectics, As I see it a eutectic is the =
=3D
result of two (to start with) materials that when mixed in different =3D
ratios will change the melting point , usually of both. The ancient =3D
Japanese potters knew materials, what rock was ground or the glaze base, =
=3D
what rock from the Kamo River prouced a source of lithium, even tho they =
=3D
didn't call it lithium, added calcium from fired oyster shells, got =3D
silica from straw ash etc. It is my way of thinking that the more you =3D
understand the interaction of your materials that you may create "Mukyo" =
=3D
the glaze of your dreams.
=3D20
If you want an easy lesson in relationship of materials do some 1, 2,3 =3D
glazes. 3 parts spar, then use flint in the glaze mix and change your =3D
other material, like whiting, barium. clay etc. Bernard Leach used 1, =3D
2. 3 glazes...it's another start for glazes. Frits etc will work for =3D
low and middle fire glazes.
=3D20
Being given a glaze isn't the reward you'll get when you develop "your" =
=3D
glaze.Keep making pots and glazes, the best ones are still in you.
=3D20
Bill Merrill
=3D20
=3D20
Earl Krueger on mon 23 nov 09
One thing I have not seen discussed in the recent
conversations on melting/eutectics is the degree of
intimacy of the components of the eutectic.
If one were to take one each of pea sized pieces of
calcia, alumina and silca and place them in the kiln
such that the three pieces touched each other I doubt
that you would see much melting at 1170 C. However
if you ground these to a 200 mesh powder you would
probably start seeing some fusion. The finer the
powder the quicker the mixture would melt.
The ultimate mixture would be a previously melted
sample where the components are now in contact
with each other at the molecular level.
Earl Krueger
Oregon, USA
Lee Love on mon 23 nov 09
On Sun, Nov 22, 2009 at 11:34 PM, Bill Merrill wrote:
> It would perhaps more beneficial for individul potters to do a =3DA0serie=
s =3D
of >fusion buttons using each material you want to test with different feld=
=3D
spars.
This is an excellent empirical way to understand the melting
qualities of different materials.
--
Lee, a Mashiko potter in Minneapolis
http://mashikopots.blogspot.com/
"Ta tIr na n-=3DF3g ar chul an tI=3D97tIr dlainn trina ch=3DE9ile"=3D97tha=
t is, "T=3D
he
land of eternal youth is behind the house, a beautiful land fluent
within itself." -- John O'Donohue
ivor & olive lewis on thu 26 nov 09
Dear Earl Krueger,
You make a valid point.
<<...One thing I have not seen discussed in the recent conversations on
melting/eutectics is the degree of intimacy of the components of the
eutectic...>>
From the Oxford Dictionary of Science and other sources of information ther=
e
are several things to consider which apply to the Eutectics featured in
Phase Equilibrium Diagrams of Oxide Systems.
1. A Eutectic Substance is a Solid Solution or an Alloy.
2. It is crystalline.
3. Its particulate components will be in the form of Ions (atoms or groups
of atoms that have gained or lost electrons) Atoms or Molecules.
4. One particle, as defined above, in a solid solution is replaced by a
different Ion, Atom or Molecule.
5. Replacement takes place so that substitution happens at crystal lattice
sites.
So you might say intimacy is at the atomic level, which seems to rule out
ingredients of a normal glaze recipe batch. Frits are out because they are
usually amorphous or glassy. Nepheline Syenite seems to qualify. Potash
felspar would not, it undergoes a Peritectic reaction (A whole new ball
game. Lets not go there. But it is important)
Please read my note to Jess McKenzie about two varieties of Eutectic. You
might research Arthur S. Watts. Much of what he wrote in the middle of last
century is published by the American Ceramics Society. His work is based on
results derived from testing for Deformation Eutectic Mixtures.
Best regards,
Ivor Lewis,
Redhill,
South Australia
| |
|
