TEAPOT, JIM CONNEL, USA
Glazed with a chrome oxide green glaze fired in a reduction atmosphere
NORTHERN SUNG DYNASTY VASE
Olive green glaze from iron oxide fired in an oxidizing atmosphere
ART 191 - ADVANCED CERAMIC HANDBUILDING SOURCES OF COLOR IN GLAZE |
A BASE GLAZE is a glaze that contains sources of the three essential components of a glaze, (SILICA, FLUX AND ALUMINA) and that contains no added color. Accordingly, it will be white or clear when fired. To achieve colored glazes, first a satisfactory BASE GLAZE is found which "fits" the clay body being used, and then tests are run adding various blends of the following metallic oxide colorants: |
METALLIC OXIDE |
% |
TYPE OF FIRING |
RESULTANT COLOR |
cobalt oxide |
1/2-2% |
gas (reduction) |
blue, blue-violet |
cobalt oxide |
1/2-3% |
electric (oxidation) |
blue, blue-violet |
iron oxide |
1/2-2% |
gas (reduction) |
jade green celadon |
iron oxide |
2-3% |
gas (reduction) |
iron yellows |
iron oxide |
3-4% |
gas (reduction) |
golden-orange |
iron oxide |
4-5% |
gas (reduction) |
brick red (khaki) |
iron oxide |
5-6% |
gas (reduction) |
brown-black (temmoku) |
iron oxide |
1/2-6% |
electric (oxidation) |
amber-greenish browns |
manganese dioxide |
5-10% |
gas (reduction) |
honey browns |
manganese dioxide |
5-10% |
electric (oxidation) |
purple, eggplant |
chrome oxide |
2-3% |
gas (reduction) |
greens |
chrome oxide |
2-3% |
electric (oxidation) |
browns, pinks, reds |
copper oxide |
2-3% |
gas (reduction) |
reds, purples |
copper oxide |
2-3% | electric (oxidation) |
turquoise blues, greens |
vanadium pentoxide |
5-10% |
gas (reduction) |
grays |
vanadium pentoxide |
5-10% |
electric (oxidation) |
yellows |
These metallic oxides are added in the amounts indicated to suitable base glazes to achieve colored glazes. Note that the type of firing employed will have a great influence on the color achieved in the glaze. To read more about the effects of firing atmosphere on glaze color go to KILNS. Here is an example of a typical base glaze formula and some possible oxide additions: |
| Feldspar | 48.9g |
|
| Kaolin | 25.1g |
|
| Dolomite | 22.4g |
|
| Whiting | 3.6g |
|
100.0g |
||
| add 1% cobalt oxide | 1.0g |
glaze color is now blue |
| OR add 3% chrome oxide | 3.0g |
glaze color is now green |
| OR add 1% cobalt oxide | 1.0g |
|
| AND 3% chrome oxide | 3.0g |
glaze color is now blue green |
TEAPOT, JIM CONNEL, USA Glazed with a chrome oxide green glaze fired in a reduction atmosphere |
NORTHERN SUNG DYNASTY VASE Olive green glaze from iron oxide fired in an oxidizing atmosphere |
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