Snow Flake redux

Glazes are fired at cone 6 in an electric kiln.

The kiln is cooled slowly, at a rate of 50 deg F an hour in the temperature interval 1850 to 1700.

It is then cooled 25 deg F an hour in the temperature interval 1700 deg F to 1650 deg F.

There is then a 1 hour hold at 1650 deg F.

Some years back, a mug with the glaze mancos_L_94_1, had the appearance of snow flakes on a glossy blue ground:

full view

glaze mancos_L_94_1 mug ~5 inches high

Even on this mug, one notes large patches of opaque white, congealed snow. In All future work this glaze was opaque white matt.

The glossy blue ground had vanashed.

Tests of a number of nearby glazes equally were opaque white matt.

I restarted the search for this snow flake glaze, with variations on the empirical formula of mancos_L_94_1, one of which hiAl_4V_4, exhibited the phenomena of "breaking" opaque matt and gloss.
This glaze has increased alkaline metals
balanced by a decrease in alkaline earths.

Not the balanced islands of matt in a sea of translucent glossy blue, but a beginning.

First step, the glaze hiAl_4V_4

full view

bowl ~6 inches in diameter



The descendants of this glaze, the grandchildren of mancos_L_94_1 have respectively
increased alumina,
replacement of some CaO by MgO, and
increase in both Alumina and Silica.

I now focus on perturbations of the base glaze, with one change only in the empirical formula.

The glaze with increase in both Alumina and Silica can be seen as an increase in the relative fraction of base in the glaze.
Alternatively, it can be viewed as a descendant of the first grandchild glaze with added Alumina, to which Silica is now added, i.e. a great grandchild of mancos_L_94_1.

second generation descendants

The changes described are the modifications to hiAl_4V_4.

glaze hiAl_4X_2

This glaze is hiAl_4V_4 with an increase in Alumina.

We observe the return of both the blue ground of mancos_L_94_1, and the near equal dispersion of opaque white and translucent glossy blue regions on the glaze surface.

We won't know if this glaze is more reproducible than its predecessor. It is however a different composition,
with the change in ratio of alkali metals to alkaline earths and the 10 % increase in Alumina.
I thus know that the phenomena of "snow flakes" on a glossy ground is not tightly confined in glaze space.

full view

cylinder bowl ~4 inches in high



glaze hiAl_4X_3

This glaze is hiAl_4V_4 with some CaO replaced by MgO.

The sharp demarcation between matt and gloss regions is gone, the entire glaze is glossier, the effect of the increase in MgO is a glossier glaze.
Interestingly the color of the glossy regions shifts from yellow back to the pale blue we'd seen in mancos_L_94_1.

full view

cylinder bowl ~4 inches in diameter



glaze hiAl_4X_5

This glaze can be seen either as hiAl_4V_4 with an increase in both alumina and silica,
or as hiAl_4X_2 (the snow flake glaze) with an increase in silica.

Except where the glaze application is thin, the glossy regions are gone, the glaze returns to the pure opaque matt white state.

We show inside and outside of this 4 inch diameter bowl:



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