Common: Al2O3, B2O3, BaO, C, CaO, CO2, CoO, Cr2O3, Cu2O, CuO, Fe2O3, FeO, H2O, K2O, Li2O, LOI, MgO, MnO, MnO2, Na2O, NiO, O, Organics, P2O5, PbO, SiO2, SnO2, SO3, SO4, SrO, TiO2, V2O5, ZnO, ZrO, ZrO2, Others

Cu₂O (Cuprous Oxide)

Family:	Colorant
Weight:	143.000
Expansion:	0.000
Fusion:	1230C

(Sources: Red Copper Oxide)

See Cupric Oxide

-Reduction firing reduces normal CuO copper oxide to Cu2O to produce bright red coloration in the reaction:

2CuO + CO -> Cu2O + CO2

-Bright red colors are usually achieved with very small amounts of copper (i.e. .5%).

-If larger amounts of copper are present, the reaction could precipitate very tiny copper metal particles (colloidal copper) in the glaze melt to yield a red color (i.e. flamb‚ or sang-de-boeuf).

-Copper luster can be produced by oxidation firing at low temperature glaze (950C) with heavy reduction cooling to leave a metallic layer of copper on the surface. 2-8% copper is required and cooling should be done in 15 minute cycles of reduction, interspersed with intervals where the atmosphere is allowed to clear. This can be carried out in cooling electric kilns by creating reduction through the introduction of flammable materials.

Properties

Glaze Color - Blue-green
Fluoride, when used with copper, can produce blue green colors.
Glaze Color - Red
Copper is well-known for its ability to produce blood-red and fire-red colors in steady reduction atmosphere firings where CuO is altered to Cu2O. See example copper red recipes in RECIPE area.
Bright red colors are usually achieved with very small amounts of copper (i.e. 0.2-0.5%) in a low alumina base with at least .4 molar equivalents of CaO and plenty of the alkalis. Tin oxide will enhance color. Use of silicon carbide in oxidation (2%) can produce red.
Glaze Color - Purple
The use of boron in a copper red reduction glaze will give a purple hue.
The following formula produces good purple at cone 10: BaO 0.1, CaO 0.5, MgO 0.1, KNaO 0.2, ZnO 0.1, B2O3 0.15, Al2O3 0.2, SiO2 3.0.
Glaze Color - Turquoise
In copper red glazes, barium additions in a high feldspar base will produce turquoise to deep blue depending on how much copper is added. Lithium contributes to the color also.
Glaze Color - Metallic
Large amounts of copper in a glaze give metallic and even graphite effects.