Copper Colors
The effect of varying the SrO:CaO balance on the color of copper within the glaze.
The four glazes are sr_Z40_PAl_MSr, sr_Z40_PAl, sr_Z40_PAl_PSr, and
sr_Z40_PAl_PPSr.
With no SrO, the glaze is black; with the first increment of SrO, the glaze is
aqua with dark spots.
We show these four glazes in order of increasing SrO, decreasing CaO. For
convenience we give below
sr_Z40_PAl_MSr 0.00 0.66
sr_Z40_PAl
0.38 0.27
sr_Z40_PAl_PSr 0.44 0.20
sr_Z40_PAl_PPSr 0.61 0.02
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 1850 deg F then a 2 hr hold at 1850 deg F
300 deg F an hour to 1750 deg F then a 1 hr hold at 1750 deg F
300 deg F an hour to 1700 deg F then a 3 hr hold at 1700 deg F
25 deg F an hour to 1650 deg F then a 1 hour hold at 1650 deg F
K2O 0.11
Al2O3 0.55
SiO2 2.99
molecular percent Silica 65.8%
added:
3% Black copper oxide
K2O 0.11
Al2O3 0.56
SiO2 2.98
molecular percent Silica 65.6%
added:
3% copper oxide
K2O 0.11
Al2O3 0.55
SiO2 3.02
molecular percent Silica 65.9%
added:
3% copper oxide
K2O 0.11
Al2O3 0.55
SiO2 3.06
molecular percent Silica 66.1%
added:
3% copper oxide
The next increment of SrO gives a greener aqua, and the
dark markings are gone. Finally, with
minimal calcium, the glaze is yet
greener, and there are the greyed yellow-green strontium markings,
which are
unrelated to the black markings seen with minimal SrO.
the molecular fraction of SrO and CaO in these four
glazes.
molecular fraction of SrO and CaO in these four glazes
Image of the glaze sr_Z40_PAl_MSr
inside
outside
Image of the glaze sr_Z40_PAl
inside
outside
Image of the glaze sr_Z40_PAl_PSr
inside
outside
Image of the glaze sr_Z40_PAl_PPSr
inside
outside
bowls are ~3.5 inches in diameter
oxidation firing to cone 10 in an electric kiln
Firing profiles
Up Fire profile cone 10
Down Fire Profile cone 10
Clay body is a grolleg porcelain from Clay Art Center in Tacoma, WA.
glaze compositions
Empirical Formula sr_Z40_PAl_MSr :
Na2O 0.22
CaO 0.66
MgO 0.01
Empirical Formula sr_Z40_PAl :
Na2O 0.23
CaO 0.27
MgO 0.01
SrO 0.38
Empirical Formula sr_Z40_PAl_PSr :
Na2O 0.23
CaO 0.20
MgO 0.02
SrO 0.44
Empirical Formula sr_Z40_PAl_PPSr :
Na2O 0.23
CaO 0.02
MgO 0.02
SrO 0.61