Iron Frequently used in high-fired glazes. In small concentrations and a reducting atmosphere, it will yield bluish-green. In high concentrations it yields a dark brown or black. In overglaze enamels it can yield a flame red or in combination with antimony, a brilliant yellow. Painted directly on the body, it can yield a black or brown.
Copper Used in lead-fluxed glazes, produces a bright green.
As a pigment applied to the body under transparent high-fired glazes in reducing conditions it could produce red, but difficult to control. Cobalt Cobalt yields a rich blue. This refers to the amount of oxygen allowed in the kiln. Reduction is produced by a carbon-rich atmosphere from which oxygen is limited, while oxidization allows a generous amount of oxygen to enter the kiln. Reduction and oxidization affect the color of bodies, glazes, and pigments.