Katharine, I printed on tiles which were only bisque-fired at about 700 C°, and had yet to receive their glazing (at 1250 C°). The tile was then to be glazed with the image on it, and when there was a transparent glazing over it, the image became really a part of the glazing, with beautiful shadows and an absolutely unique quality. The only pigment with which I succeeded to do this at this termparature was cobald oxide, so the image was blue. Iron oxide worked without a pransparent layer over it; the glass over it somehow "gnawed it away". I suspect it would work, however, at 1050 C°, as would probably other pigments.
Tiles are quite fragile and porous when bisque-fired, and suck up instantly any fluid (your tongue sticks to them when it touches the surface). I had to coat over this surface in order to be able to print an image on it, which, however, made the subsequent glazing layer much more difficult to apply. That was the problem I was still fighting with when I had to abandon my experiments for the time being.
I might, however, be able to pick them up again in some time.