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glaze course lesson 6 part one

updated mon 31 jul 00


hal mc whinnie on sun 30 jul 00


Completion of the review of Chinese glazes

One reason for our concern with high fire Chinese glazes is that they are of
simple glaze structure, at the very heart of the seger method, and they were
the historical basis for much of our current glaze technology.

PEACH BLOSSOM cone 9 reduction
Neph syn 166
Custer spar 35
Kaolin 8
Flint 80
Colemanite 46 [gertsley borate]
Whiting 36
Zinc oxide 6
Copper oxide 2
Tin oxide 4

TURQUOISE cone 9 reduction
Custer spar 157
Flint 72
Whiting 9
Soda ash 68

Seger analysis
Sio2 2.98
Al2o3 0.27
Cao 0.10
Mgo 0.01
K2o 0.18
Na2o 0.71

Note that this is a standard seger formula for a cone 8-10 glaze, it is very
high in feldspar and low in whiting which may be a problem. It should be a
highly gloss glaze and have a great tendency to run, somewhat like the
effect of a Chinese celadon.

These above comments are what one can make by an inspection of any glaze
formula of course the real test is in the glaze test.

Percent by weight
Flint 23.53
Whiting 2.94
Soda ash 22.22
Potash spar 51.31

Let us look at the simple proportions of this glaze, it is basically a
25-25-50 glaze and again does seem to be high in feldspar.

OIL SPOT cone 9 reduction
Albany clay 65
Kaolin 5
Custer spar 20
Whiting 10

Seger analysis
Sio2 2.68
Al2o3 0.53
Cao 0.48
Mgo 0.19
Feo 0.14
K2o 0.15
Na2o 0.04

Note that this glaze is a little low in silica for a cone 9 glaze. It is
however high in alumna which should retard glaze flow and the melter [parts
of the ro factors] seem to be very well balanced and not skewed like our
turquoise glaze.

Also note that all glazes are balanced according to the seger analysis and
this really tells rather little about the difference is the glaze.
They need to be balanced according to the seger formula but the variations
within this balance is at the guts of glazemaking as I will try to show in
the balance of this lesson and in the lessons to follow.