Lithophanes are porcelain pictures made by casting clay in layers of various thicknesses. When a piece is held to the light, a picture of light and shadow is seen through it. The darker and lighter parts of a lithophane are made by varying the thickness of the porcelain. Most lithophanes date from the 1825-1875 period. A few are still being made. Many lithophanes sold today were originally panels for lampshades.