It was totally new thing from all I'd learned. The ceramic tile can't "hold" the paint (like paper) for the tile has no pores at all. It was a glazed tile. So it seemed that the paint just slipped away. The colour will look stronger and darker after the firing, so we have to be careful in choosing the right colour. And if we paint a darker colour underneath a lighter one, after the firing the darker colour will revealed (except that was what we want).
Here what I paint before the firing process:
After the firing process: