Expert: Sam Kelly - 2/16/2010

Question
Hello!  I am curious to learn if cobalt carbonate, in a small quantity, can be used as a colorant in an ovenware clay recipe?  The recipe I have uses a small amount of red iron oxide as a colorant, and I was interested in attempting a lovely blue--simply for variety. Would leaching be a problem on an unglazed pizza slab, for example?  Would the blue fade eventually?  Your thoughts and knowledge are appreciated.

Answer
Remove the Red Iron Oxide as that is the colourant and replace it with the Cobalt Carbonate. However usually only 1gram per 100grams of BASE is all that is needed.

BASE is your glaze WITOUT any colourant in it(RIO - Co. Carb.).

It will not fade, leach or anything alse useing these colourants, it's your base glaze that is the problem if this happens.

Good thing about Co.carb is that wether gas or electric - oxidation or reduction, it will always be BLUE.

Sam