COOX
Black powder; fires blue · A colourant for glazes, slips and clay bodies · The more concentrated of the two cobalt powders — more cobalt per gram · Roughly two-thirds the amount of cobalt carbonate · Coarser than the carbonate, so a glaze carrying it needs sieving · Blended with iron, and often manganese, as a route to black
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Cobalt oxide is a black powder that fires blue, and the more concentrated of the two cobalt powders a recipe can call for. It colours glazes, slips and clay bodies.
Cobalt oxide is a black powder that fires blue, and it colours glazes, slips and clay bodies. Cobalt reaches a recipe as either this oxide or the carbonate, and the oxide is the more concentrated of the two. A very small addition already reads as a medium blue in a clear glaze, and a heavier one takes it to a deep near-black — a true black needs iron, and usually manganese, alongside it. It carries about half again as much cobalt per gram as the carbonate, so a recipe written for carbonate needs roughly two-thirds as much oxide. It is also the coarser of the two and will not disperse evenly on its own, so a glaze carrying it wants sieving; without that the colour arrives as blue specks and mottling rather than as a flat blue. Which blue turns up depends heavily on the glaze around it, as it does for the carbonate. Blended with iron oxide, and often manganese as well, it is one of the standard routes to a black, though published black recipes vary a great deal in how much cobalt they carry.
