One oxide, multiple colors?
Among the metallic oxides craftsmen use as ceramic colorants, iron oxide can be deemed as the most important.
This type of oxide is naturally present in most clay in the form of Fe2O3. When fired in oxidation kiln, we can achieve multitude color tones depends on the amount of iron oxide in the glaze, ranging from light yellow to dark brown. The color produced is also partly the result of other oxides present in the glaze.
Effortless as it might seem, that vitreous layer of glaze coating our earthenware is a combination of many different oxides that fuse and interact in the kiln to form the final design and coloring. In reduction firing, oxygen will be pulled out from ferric oxide (Fe2O3) which converts to ferrous oxide (FeO).
This method can produce celadon green glaze (which is interestingly not in the color range mentioned above) and turn it into a powerful flux. Fluid glaze always bring with it many surprise outcomes and will often slip down to the base of the product and even flow onto the kiln shelf. This results in sharp plucking that need to be broken off and sand off carefully.
Sometimes, not all oxygen is sucked out from ferric oxide so that we can attain a mixture of ferric and ferrous oxide called magnetite (Fe3O4). In this case, it will bring about a curious effect of little bubbles on the glaze surface.
With just iron oxide, we can already deliver plenty different effects. Glaze mixing is the art of balancing between art and science, experience and inspiration, with the help of Prometheus gift.