Color in glazes containing Chrome Oxide
cone 10 oxidation
Firing 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
Clay body is a grolleg porcelain from Tacoma Clay Art Center.
glaze composition
I have four glazes which differ primarily in the relative proportions of the alkaline earths:
In their respective empirical Formula's these glaze have in common:
Alkali metals .5
Al2O3 .5
SiO2 3
The breakdown of the alkali metals is:
K2O .22
Na2O .23
Li2O3 .05
In the empirical Formula:
The relative proportions of the alkaline earths in these glazes:
paperWhite_ZO_0 the ratios CaO:MgO:SrO are 1:3:6
paperWhite_ZO_1 has negligible MgO
the ratio CaO:SrO is 2:3
paperWhite_ZO_2 has negligible MgO
the ratios CaO:BaO:SrO are 1:2.333:5
paperWhite_ZO_3 has negligible MgO
the ratios CaO:SrO 1:3.5
These glazes contain .2 % by weight Chrome Oxide.
I was intrigued by the
range of color available with small concentrations off Chrome Oxide.
It
would seem that Chrome is a versatile glaze coloring agent.
The dark splotch in these pots is an overglaze decoration, a leaf had been
embedded in the glaze, removed, and the impression stained with EP Kaolin.
The pots are small bowls ~4 inches in diameter.
paperWhite_ZO_0 with 0.2 % Chrome oxide
paperWhite_ZO_1 with 0.2 % Chrome oxide
paperWhite_ZO_2 with 0.2 % Chrome oxide
paperWhite_ZO_3 with 0.2 % Chrome oxide
Commentary
Note that paperWhite_ZO_0 and paperWhite_ZO_2 with the least CaO (.05, resp .06 molecular equivalents in their empirical formula).are varigated semi-matte glazes exhibiting a variety of yellows, browns and blue greens.
By contrast paperWhite_ZO_1 and paperWhite_ZO_3 with substantially higher CaO
(respectivel .19 an .11) have a bright green glossy phase,
in addition to the
blues and browns seen in their matt phases.
Is the change in color the result of the greater CaO, or rather the result of the glossy texture of the glaze?