ART 186 - INTRO TO CERAMICS

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:

HIGH ALUMINA MAT
 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 Connell

TEAPOT, JIM CONNEL, USA

Glazed with a chrome oxide green glaze fired in a reduction atmosphere

 Northern Sung Celadon Vase

NORTHERN SUNG DYNASTY VASE

Olive green glaze from iron oxide fired in an oxidizing atmosphere


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