Lawrence Ewing on fri 1 aug 97
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Hi Susan,
I Have not read the article you mentioned as the latest copy of Ceramics
Technical has not reached this far South (Dunedin N.Z.) but I have worked
extensively with students using Ian=B9s system and have recently had =
discussions
with him about using any recipe as a starting point for creating quadraxial
blends in which the alumina and silica are varied from a minimum in corner C
(bottom left corner).
The process is really simple particularly if you have the Glaze Software =
program
called Matrix enables easy manipulation of recipes or formulae and which =
will
create the final blend after the corner glazes have been established.
Say you have a favourite glaze and you wish to explore the variations that =
can
result from changing the silica and alumina content using the original =
recipe as
the starting point. A four cornered quadraxial blend is used for this =
exercise.
Step 1 Create the corner C glaze (bottom left corner of the quad) by =
removing
from the recipe all clay materials and all silica. Make sure after this =
that
you make the amounts in the remaining glaze total 100.
This leaves a list of materials which are the sources of flux in the glaze.
There may be some alumina and silica still available if such materials as
Feldspar or Talc etc are the sources of flux in the original recipe.
Step 2 Create the corner A recipe in the quadraxial blend (top left hand
corner) by adding as much clay as you wish. For stoneware glazes Ian adds
sufficient clay to increase the Corner C recipe=B9s alumina content by 0.6
molecules. If your corner C glaze was converted to a recipe totalling 100 =
then
you could be adding around 95 parts by weight of clay to achieve the 0.6 =
mols
increase for alumina.
Step 3 Create the corner D recipe (bottom right corner of the quad) by =
adding
the material silica to the corner C glaze. Ian=B9s addition for stoneware =
glazes
is around 4 mols. Again with corner C glaze totalling 100 you may need to =
add
135 parts by weight of Silica material to achieve the 4 mol increase in =
silica
for corner D.
Step 4 Create the corner B recipe by adding sufficient silica to the =
previously
created corner A recipe to increase its silica content by 4 mols. If when =
you
created the A recipe you did not convert it to total 100 then you may need =
to
again add as much as 135 parts by weight of silica material to the A recipe.
Step 5 Convert the recipes so that each totals 100.
Any glaze may be used as the starting point in this process. The =
appropriate
amount of increase for alumina and silica in the process would vary =
depending on
the firing range for the original glaze.
I hope this explanation helps Susan. I have found Ian Currie=B9s systematic
approach extremely useful in the search for understanding the basics of =
glaze
technology. Your Matrix glaze software makes the process described above =
very
easy by either manipulating recipes to achieved the desired oxide levels or
working directly at the formula level then creating the glazes from the =
formulae
for the corners. Matrix will also create the whole blend in the form of a
worksheet enabling the mixing and analysis of the resulting blend.
Regards,
Lawrence Ewing
Lecturer in Ceramics
School of Art
Otago Polytechnic
lewing=40clear.net.nz
21 Slant St
Careys Bay
Dunedin
NEW ZEALAND
ph (03) 472 8801
Author of MATRIX Glaze Calculation Software for Macintosh
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