GLAZE COLOR

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	%	FIRING TYPE	FIRED COLOR
COBALT	1½	reduction	blue, blue-violet
COBALT	1½	oxidation	blue, blue-violet
IRON	½-2	reduction	jade green, celadon
IRON	2-3	reduction	straw yellow
IRON	3-4	reduction	golden orange
IRON	4-5	reduction	brick red, japan khaki
IRON	5-6	reduction	brown-black, temmoku
IRON	½-6	oxidation	amber to brown
MANGANESE	5-10	reduction	purple, eggplant brown
MANGANESE	5-10	oxidation	honey browns
CHROME	2-3	reduction	green
CHROME	2-3	oxidation	brown, pink, red, yellow
COPPER	2-3	reduction	red, purple
COPPER	2-3	oxidation	turquoise blue, green
VANADIUM	5-10	reduction	gray
VANADIUM	5-10	oxidation	yellow

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

This is a classic BASE GLAZE. Note that there are sources of Silica (in the Feldspar and the Kaolin), sources of Alumina (also in the Feldspar and the Kaolin), and fluxes (the Dolomite, the Whiting, and flux present in Feldspar). It's color is white.

To turn this white, base glaze into a colored glaze we simply add colorants from the list above, either singly or in combinations. For example:

To this base glaze, add 1% cobalt oxide (in this case 1% of 100g is 1g) and now the glaze color when fired is blue.
OR add 3% chrome oxide (in this case 3% of 100g is 3g) glaze color is now greenand the fired glaze color is now green
OR add 1% cobalt oxide (in this case 1% of 100g is 1g) AND 3% chrome oxide (in this case 3% of 100g is 3g) and the fired color is blue green.
Oxides can be combined in complex mixtures to create unusual colors. Glaze testing is a challenging and rewarding area of study for any ceramic artist.

TEAPOT, JIM CONNELL, USA, 2005

Porcelain, wheel thrown and glazed with a chrome oxide green glaze fired in a reduction atmosphere

lajvardinaewer161

LAJVARDINA EWER, PERSIA, 1210 CE

Ewer (Pitcher), Wheel thrown earthenware with turquoise blue (lajvardina) glaze from Kashan, a city which specialized in luster ware. The turquoise color of the glaze results from copper oxide fired in an oxidation atmosphere.

Sungceladonvase4x5

NORTHERN SONG DYNASTY VASE, CHINA, 1050 CE

incised porcelain with amber brown glaze from iron oxide fired in an oxidizing atmosphere

songrucicada647

SOUTHERN SONG DYNASTY, 'RU' WARE CELADON, 1100 CE

Close up of the cicada's wing pattern in the blue-green celadon glaze. Iron oxide impurities in the local glaze minerals result in this prized color when fired in reduction atmospheres.

mingblueandwhiteplate555

MING DYNASTY BLUE AND WHITE PLATE, CHINA, 1430 CE

Porcelain platter, wheel thrown with cobalt oxide painted design. Cobalt is a reliable blue pigment in most firing atmospheres and temperatures, as in this example, fired at highest temperatures in a reduction atmosphere. .

minganhuafooted677

MING DYNASTY STEM CUP, CHINA, 1375 CE

Porcelain cup, wheel thrown in two pieces and joined. Inside the foot is a hidden carved design (called 'an hua'), which can only be seen when the cup is held to the light and the carved, translucent porcelain allows the light to penetrate. The blood red glaze results from copper oxide added to the glaze and then firing in a reducing atmosphere.

meissenogpalette1409

MEISSEN COLOR PALETTE, GERMANY, 1725 CE

European porcelain was developed hundreds of years after the Chinese had perfected it during the Song Dynasty. The glaze alchemists at Meissen were able to create an almost full palette of overglaze colors to use with their famous porcelain tableware and display pieces that graced the tables and emptied the treasuries of European royalty.

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