Made around 1980. Clay is Plainsman H440G. Fired to cone 10R. Glaze is rutile blue (G2571A with rutile and a little cobalt added).
G2571A - Cone 10 Silky Dolomite Matte Base Glaze
A cone 10R dolomite matte having a pleasant silky surface, it does not cutlery mark, stain or craze on common bodies