Copper Red
My first copper red was seen here:
Next:
I show a glaze of Robert Tichane, from his book "Copper Red Glazes".
I had guessed that the glaze as given by Tichane would be too refractory to
give copper red in my firing, so I also tested a modification which I expected
to be more fluid.
I replaced some CaO with Li2O, but then also increased the alumina to get my
glaze tichane_Z1C_1. I wanted a glaze that was fluid but not 'liquid like
water'. To accomplish that, I added some alumina to compensate for the
lithia. The result was more fluid and red rather than blue.
The local reduction is produced by the inclusion of 1 % of 1000 mesh silicon
carbide in the glaze recipe.
These glazes, as all my glazes, are mixed with CMC gum which aids in
maintaining the silicon carbide in suspension.
cone 10 oxidation
Firing profile
Up Fire profile
150 deg F an hour to 250 deg F
400 deg F an hour to 2050 deg F
120 deg F an hour to 2250 deg F
60 deg F an hour to 2310 deg F with a hold of 20 minutes at 2310 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.
K2O .20
Al2O3 .33
SiO2 3.7
molecular percent Silica 70
I added 1 % silicon Carbide and 1 % Copper Carbonate to the above
The glaze tichane_Z1C_0 is derived from the glaze given by Tichane as his
"base" copper red glaze. I computed the empirical formula of that glaze,
K2O .26
Al2O3 .42
SiO2 4.1
molecular percent Silica 71 %
I added 1 % silicon Carbide and 1 % Copper Carbonate to the above.
This glaze is derived from the glaze above by replacing some CaO with Li2O,
and increasing Al2O3. The change in relative proportion of K2O and Na2O was
a
The glaze tichane_Z1C_1 is more fluid than the original tichane_Z1C_0,
it also has higher alumina.
tichane_Z1C_0 is a lovely blue glaze, if it weren't judged a failed copper red
glaze.
tichane_Z1C_1 is heavily pinholed, the next step is to remedy that defect.
Clay body is a grolleg porcelain from Tacoma Clay Art Center.
glaze compositions
Empirical Formula glaze tichane_Z1C_0 :
Na2O .24
CaO .50
MgO .02
ZnO .04
B2O3 .19
SnO2 .05
which included Pemco Frit 25, then recreated the glaze tichane_Z1C_0 from that
empirical formula.
Empirical Formula glaze tichane_Z1C_1 :
Na2O .19
Li2O .16
CaO .32
MgO .02
ZnO .05
SnO2 .05
secondary effect of the computations.
bowls are ~ 4 inches in diameter
glaze tichane_Z1C_0
glaze tichane_Z1C_1
Remarks
Copper red glazes must be rather fluid, but
not
necessarily low in Alumina.