Copper Colors
This glaze is a variegated purple and white micro-crystalline matte. If thin
the color dissapears, else if sufficiently thick,
This is derived from David Tsabar's cone 9 waxy matte
copper red glaze. It is the tile in the upper left corner of the
biaxial test.
The derived glaze, tsabar-harris-red-PSiAl, has no tin oxide, increased
alumina and silica, and some
inside of bowl:
Outside of bowl:
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 2310 deg F with a hold of 20 minutes at 2310 deg F
300 deg F an hour to 1750 deg F then a half hour hold at 1750 deg F
300 deg F an hour to 1700 deg F then a Three hour hold at 1700 deg F
25 deg F an hour to 1650 deg F then a one hour hold at 1650 deg F
This glaze has 0.5% Copper Carbonate and 0.5% silicon carbide added
K2O 0.24
Al2O3 0.62
SiO2 3.47
molecular percent Silica 67.8%
It seemed that the original glaze tsabar-harris-red, was overfired at a hot cone
10, because it became glossy if thickly applied.
Replacing some CaO with SrO also can often stiffen a glaze. It would seem, I
can't restrain myself to only one change.
larger maroon fragments
dominate.
of the CaO replaced by SrO. It is then
fired to a hot cone 10.
tsabar-harris-red-PSiAl
bowl is ~3 inches in diameter
oxidation firing to cone 10 in an electric kiln
Firing profiles
Up Fire profile
Down Fire Profile
Clay body is a grolleg porcelain from Tacoma Clay Art Center.
glaze compositions
Empirical Formula glaze tsabar-harris-red-PSiAl :
Na2O 0.07
CaO 0.41
MgO 0.02
SrO 0.19
ZnO 0.07
Fe2O3 0.02
Remarks
For that reason, I increased the
silica and alumina, maintaining contant the silica:alumina ratio. This is
equivalent
to deceasing the fraction of basic components of the glaze.
Occasionally the result of
this, as in this case is interesting.