Interaction of Two Glazes

cone 10 oxidation

Firing profile

Up Fire profile

150 deg F an hour to 250 deg F

400 deg F an hour to 2050 deg F

120 deg F an hour to 2310 deg F with a hold of 20 minutes at 2310 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 hot cone 10 firing.

This is my usual firing profile

I wanted to reproduce the marvelous effect of the base glaze flowing through the inlay seen here:

July 2018 Cone 10 crystals

The effect in that firing was the result of an exageratedly long firing between cone 5 and cone 10. The cones in the firing said cone 11.
The base glaze on that pot, and on several other pots ran. In addition to the uncontrolled running,
I didn't like the effect on my saturated iron glazes. The next step for me, which I show here is to alter the glazes,
with the intent to get a flow in my usual firing at cone 10.

Here I modify only the inlay glaze, making it more fusible. I wanted to get an effect that might be usable on the outside of a pot.

Next I will make the base glaze more fusible as well. That will be trickier, as too fusible will again result
in flowing off the bottom of the pot.

The two glazes below ran together, the crystals of the base glaze show as a counterpoint to the streaks created by the runs of the inlay glaze.

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

I show details of the flows on a bowl ~6 inches in 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-Z12:

K2O        0.32
Na2O        0.18
Li2O        0.00
CaO        0.37
MgO        0.13

Al2O3 .56
Fe2O3 .23

SiO2 5.14

molecular percent Silica 74 %

Note: CandaceBlackB-Z12 has some cobalt added

The markings on the inside 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 markings

full view

Image of the whole piece