Black gosu Inlaid Wine Glass — Handmade Japanese Glass by Riso KilnThe iron rich glaze on this cup darkens in the kiln and pools at the foot, leaving a surface that reads differently depending on how the light falls. The depth comes from the firing, not from any added decoration. Riso Kiln forms and firing each cup by hand in Japan, working at a pace that allows every piece to be made individually. The result is a cup that carries the marks of its making never perfectly uniform, always consistent in character.