copper Red
Here are three local reduction copper glaze. These glazes are neither as high
in silica nor as fluid as the usual copper red glaze.
inside of bowl:
Outside of bowl:
inside of bowl:
Outside of bowl:
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
The glaze with added .5% copper carbonate, 2% tin oxide, and 1% silicon
carbide.
K2O .09
Al2O3 .43
SiO2 3.13
molecular percent Silica 68%
The glaze with added .5% copper carbonate, 2% tin oxide, and 1% silicon
carbide.
K2O .08
Al2O3 .48
SiO2 2.65
molecular percent Silica 64%
The glaze with added .5% copper carbonate, 2% tin oxide, and 1% silicon
carbide.
K2O .13
Al2O3 .48
SiO2 2.64
molecular percent Silica 64%
These are non-traditional formulations for a copper red glaze; these glazes
have lower silica:alumina ratio and higher alumina
The effect of lower silica:alumina ratio and higher alumina is higher
viscosity. Increased viscosity reduces oxygen movement
The use of a local reduction agent to produce colloidal copper is a one time
event at the time of the decomposition of the silicon carbide;
The first glaze, cuRed_Z20_0, is the most fluid of these glazes.
It is a bluish red; and displays the least
The pair of glazes alexanderBowl_Z15_0; and alexanderBowl_Z15_1 have
the same silica:alumina ratio and alumina and both have
However alexanderBowl_Z15_1 has higher alkali metals; so, as expected, is a
more fluid glaze.
As seen in the second pair of pictures, alexanderBowl_Z15_0 is a mixed
lilac and grey-aqua.
alexanderBowl_Z15_1, equally mixed, is red and grey-green, as seen in the last
pair of pictures.
The first of
these glazes is nearly a full gloss, is maroon, with only a slight overlay of
grey white frosty tracings.
The other two glazes, with lower alkali
metals, and lower silica are microcrystalline semi-matte glazes and are mixed
red and grey green.
Glaze cuRed_Z20_0 with copper carbonate
Glaze alexanderBowl_Z15_0 with copper carbonate
Glaze alexanderBowl_Z15_1 with copper carbonate
bowls are ~4 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 cuRed_Z20_0 :
Na2O .2
CaO .27
MgO .08
SrO .28
ZnO .08
SnO2 .05
Empirical Formula glaze alexanderBowl_Z15_0 :
Na2O .05
CaO .7
MgO .17
Empirical Formula glaze alexanderBowl_Z15_1 :
Na2O .05
CaO .63
MgO .19
Remarks
than is usual in copper red
glazes.
into and within the
glaze. As a result colloidal copper particles are not as rapidly
re-oxidized.
as a
result, re-oxidation of the copper is not easily controlled.
of the cloudy grey second
phase, but has streaky incomplete coverage, especially on the outside where
the glaze
application was thinner. This is seen in the first two pictures.
a prominent grey-aqua
second phase.