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:
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.
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.
The changes described are the modifications to hiAl_4V_4.
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.
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.
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: