Firing

cone 10 oxidation

Large crystals seen on the surface of a glaze

Firing profile

Up Fire profile

150 deg F an hour to 250 deg F

400 deg F an hour to 2100 deg F

120 deg F an hour to 2240 deg F

60 deg F an hour to 2270 deg F with a 20 minute hold at 2270 deg F

30 deg F an hour to 2300 deg F with a hold of 30 minutes at 2300 deg F

Down Fire Profile

A half hour hold at 1750 deg F

A three hour hold at 1700 deg F

slow downfire at 25 deg F an hour in the interval 1700 deg F to 1650 deg F

A one hour hold at 1650 deg F

The cones show this as a cone 11 firing.

The downfire part of this firing profile differs little from my usual downfire. The upfire profile was extended near
peak temperature, to iron out the differences between the appearance of glazes on small and large pots.
It did, but at the expense of the overall crystal growth in these high alkali metal saturated iron glazes.
The new crystals a the interface between the two glazes was as unexpected as the loss of the
primary crystals in the glaze.

The two glazes below ran together, the crystals appear at the interface of this flow. Neither of these glazes separately has shown these crystals.

Clay body is a grolleg porcelain from Tacoma Clay Art Center.

I show details of the crystals on a bowl ~8 inches in diameter. The largest of the crystals are ~3/8 inch diameter,
I also show a picture of the bowl.

glaze composition of the two glazes

Emperical Formula satIron_ZG_H_0:

K2O        0.01
Na2O        0.44
Li2O        0.32
CaO        0.17
MgO        0.06

Al2O3        .5
Fe2O3        .2

SiO2        2.74
P2O5        .045

molecular percent Silica 61 %

Emperical Formula candaceBlackB:

K2O        0.32
Na2O        0.15
Li2O        0.00
CaO        0.39
MgO        0.14

Al2O3        .62
Fe2O3        .24

SiO2        5.36

molecular percent Silica 74 %

Note: Candace Black has some cobalt added

The markings on the outside of the deap bowl are a second glaze inlay. The glaze is filled in to an area that had been masked prior to
the pouring of first layer of glaze. It was then waxed with an emulsion wax prior to
stripping the mask.

Close up Images of various of the crystals

Image of the whole piece

bowl with glaze satIron_ZG_H_0 and glaze inlay CandaceBlackB

Note that the bowl was distroyed by flow of glaze gluing it to kiln shelf.