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val cushing ash glaze c6

updated thu 31 may 01


AKitchens on tue 29 may 01

A Plea to the Glaze Masters:
I have a large tile project I am about to finish. I am
raw glazing and single firing cone 6 oxidation.
Three weeks ago I made two gallons of a glaze that
I have previously made and tested in several Cone 6
Ox. electric firings. I haven't made this quantity of this
glaze so I never noticed this problem before.
I began glazing the tile pieces and saw small twig like
particles in the glaze. I had previously meshed (80m) the
glaze several times when making it three weeks before
so I glazed several more pieces and discovered more
of the mysterious particles. I brushed them off the
glazed pieces and meshed the glaze again
and found about 2 cups of these particles. I rinsed them
and looked at them under the microscope and discovered
a crystal formation. To the naked eye they look like sharp
dark gray iron filings.
I had half of the (un bisqued) tiles in the panel already
glazed and decided to continue to glaze the rest of the
panel to keep consistency on the piece. My fear of course,
is that the crystals are a necessary (now lost) element in
the glaze. I am firing it right now, with several prayers to
the kiln god, since it is a commission.
Can anyone tell me what is growing in this
formula? Have I lost the glaze with this
crystallization occurring?
Any help on or off line would be appreciated.
Humble thanks for your wisdom and input.
Nan Kitchens

The glaze and notations are from Val Cushing's book.
Val Cushing's VC G 4
Cone 5-6, Ox or Red, Tested

Wood Ash 50.
I used unwashed, Oak and Hickory 80 mesh
Gerstley Borate 20.
Whiting 12.
EPK 08.
Flint (I used Silica) 10.
Total 100.

Unity formula from Cushing's book:
K2O .058
Na2O .036
CaO .821
MgO .085
Al2O3 .039
B2O3 .100
P2O5 .015
SiO2 .337

Est Thermal Exp. 124.88 x 10-7/C degrees
Si:Al 8.6:1