Fired in a standard decal firing. The glaze on the tile has helped fuse it to a glossy surface. Has worked well except for adhesion problems during application (because the porous body adsorbed all the water immediately). If the tile had been soaked previously it would have been better.
This process is done by printing a design (using ceramic inks) onto a film coated decal paper, drying it, then transferring the film to the fired ware. But beware of problems.