Copper Red Electric Firing

I show two copper red glazes, fired in an electric Kiln. The two glazes differ only in the amount of silica each contains,
as shown in the Empirical Formula.

cone 10 oxidation

The Firing profile

Up Fire profile

150 deg F an hour to 250 deg F

400 deg F an hour to 1800 deg F

300 deg F an hour to 2050 deg F

120 deg F an hour to 2300 deg F

20 minute hold 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 10 firing.

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

glaze compositions

Empirical Formula glaze cu-red-Z1N-0 :

high silica glaze

K2O        .18
Na2O        .18
Li2O        .15
CaO        .24
MgO        .01
SrO        .20
ZnO        .04

Al2O3        .37

SiO2        3
SnO2        .04

molecular percent Silica 68%

add:

Copper Carbonate 0.5%
Silicon Carbide 1%

Empirical Formula glaze cu-red-Z1N-1 :

low silica glaze

K2O        .18
Na2O        .18
Li2O        .15
CaO        .24
MgO        .01
SrO        .20
ZnO        .04

Al2O3        .37

SiO2        2.5
SnO2        .04

molecular percent Silica 63%

add:

Copper Carbonate 0.5%
Silicon Carbide 1%



glaze cu-red-Z1N-0

high silica glaze

full view

full view

bowl is ~4 inches in diameter


glaze cu-red-Z1N-1

low silica glaze

full view

full view

bowl is ~ 4 inches in diameter



Remarks

Note that the low silica glaze shows little copper red, and is otherwise a pale turquoise. I don't know if this is an artifact of
firing local copper red glazes in an electric kiln.

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