| Description |
CoO is a metallic coloring oxide that produces blue in glazes at all temperatures (unless in very high percentages where it will be black). Black Cobalt Oxide is the principle source of CoO used in glazes, glass, and enamels. Cobalt is the most powerful ceramic colorant and it is stable in most systems. Like copper, it melts very, very actively in oxidation and if it is mixed into a fluid frit base in high enough a percentage, it will completely crystallize during cooling.
Cobalt is also useful as a body and slip stain (see the oxide CoO oxide for more information). However, it is very very expensive, this severely limits its practical use in many things.
This material can be found in technical and ceramic grades. Cobalt will often produce glaze specking if it is not thoroughly sieved or ball milled to distribute the particles. Also, there is some inconsistency in commercial products, different batches or materials from different suppliers will vary in the amount of specking. Cobalt carbonate tends to disperse better in glazes to give even blue coloration because it is not as powerful and produces some glaze blistering problems. A high cobalt stain is also an alternative. |