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lesson five glaze course part one july 26

updated thu 27 jul 00


hal mc whinnie on wed 26 jul 00


A continuation with the seger formulas
Matt glazes for cone 10 reduction

I have a computer program by Richard zakin, which is very useful as a means
of analysis, once a seger formula has been converted into a gram batch. The
zakin program describes the glaze in plain language and offers suggestion as
to how to modify the formula.
Unfortunately Richard zakin has not to my knowledge marketed the program. I
may try to write to him to see if I have his permission to copy the disk,
which he gave me some years ago.

For this lesson I have chosen three Matt glazes because they tend to have a
different structure from the gloss glaze to be reviewed in part two of this
There is far more kaolin and flint and while unite has been maintained in
the ro elements they are a much smaller percentage of the glaze. These
glazes also offer an option to the use of barium as a matting agent for high
fire reduction glazes.

Formula analysis blue green Matt for cone 10 reduction

186 flint
54 kaolin
8.4 magnesium carb
11.04 petalite
6.8 soda spar
65 whiting
6.8 zinc oxide
2.4 copper oxide
Melter power high
Melter amount low
Sio2 75.45
Al2o3 7.98
Melter 16.57

"Because it is low in flux this category encourages mat or dry surfaces.
Because it is low in alumna glazes in this category will flow. This is the
category of flowing mat glazes.

Seger formula for blue grey stony Matt glaze

[Note how the name of the glaze almost perfectly fits the description from
the Zakin analysis quoted above.]
Nao . 065 al2o3 0.35 sio2 3.10
k2co3 .08
Cao . 65
Mgo . 10
Zno . 85
Cuo . 02

This formula demonstrated the high amount of silica, which can be found in a
Matt glaze.

Griffin dark-speckled green Matt glaze

While the structure of the following Matt glaze is quite similar to our last
example, note how the colorants are employed to give the color and texture

Sodium carb 21
Pearl ash 20
Whiting 50
Barium carb 19
Chrome oxide 1.52
Manganese 3.48
Kaolin 202
Flint 120

Melter amount very low
Melter power high
Silica high
Alumna high
Melter very low
"Recipes of this sort are composed mostly of flux clays and glassmakers with
very little flux. Typically they are either high in clay [and are engobes or
slips] or are high in feldpars. Their high alumna amount insures that they
do no flow.