Copper Colors
Application thickness influences the final color of this glaze. If thin, this
glaze is a variegated golden yellow-brown
This glaze is fired in an electric kiln with no local reducing agent, showing
that copper can produce yellow without reduction.
This firing, in addition to having a slow downfire, also has a slow upfire.
The peak temperature is lowered in order to avoid
inside of bowl:
Outside of bowl:
150 deg F an hour to 250 deg F
400 deg F an hour to 1770 deg F
300 deg F an hour to 1850 deg F
120 deg F an hour to 2130 deg F
13 deg F an hour to 2180 deg F with a two hour hold
13 deg F an hour to 2210 deg F with a three hour hold
300 deg F an hour to 1900 deg F then a three hour hold at 1900 deg F
300 deg F an hour to 1850 deg F then a Three hour hold at 1850 deg F
This glaze has 1.5% Copper Carbonate added
K2O 0.13
Al2O3 0.71
SiO2 3.25
molecular percent Silica 65.5%
Not the intended, yet an interesting glaze, both the color and texture.
Is the color that of cuprous oxide? If so, how did copper in the lower
oxidation state occur with no reduction of any form?
This glaze is underfired, as shown by the intense crazing.
This is a cone 10 firing, at a temperature which with a faster rate of heating
in an electric kiln would be cone 8.
I do not know why underfiring would result in a lower oxidation state for the
copper.
micro-crystalline matte. This is
best seen in a broad swath on the outside near the rim. If application
thickness
increases, it becomes green with a spattering of yellow-brown, and
if it is applied even more thickly, green dominates.
the retarded upfire
causing the kiln to reach a higher cone.
copperYellow_Z24_0
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 copperYellow_Z24_0 :
Na2O 0.42
CaO 0.24
MgO 0.11
SrO 0.10
Remarks
Chemical reactions depend on absolute
temperature as well as heat work.