These have to be seen to be believed, it is the deepest, richest blue we have ever produced. This is Plainsman M340 fired to cone 6. Black-firing L3954B engobe (having 10% Burnt (not raw) Umber instead of the normal 10% Zircopax) was applied inside and partway down the outsides (at the stiff leather hard stage). The incising was done after the engobe dried enough to be able to handle the piece. The glaze is Alberta Slip rutile blue. Firing schedule: Cone 6 drop-and-soak.
Metal oxide powders are used in ceramics to produce color. But a life time is not enough to study the complexities of their use and potential in glazes, engobes, bodies and enamels.
GA6-C - Alberta Slip Rutile Blue Cone 6
Plainsman Cone 6 Alberta Slip based glaze the fires bright blue but with zero cobalt.