Made using porcelain fired to cone 11+. This is a splendid demonstration of translucency. Without a back-light it is just a white slab. But the varying thickness in the porcelain determine the amount of light that passes at any given spot, thus producing the design.
Standard porcelains used by potters and for the production of sanitary and table ware have surprisingly similar recipes. But their plasticities vary widely.
A highly sought after property in porcelain, they are fired close enough to melting to pass considerable light. It can be very difficult to fire translucent ware without it warping.