This silver belt buckle was cast in a cuttlefish bone. The rippled texture that you see is inherent in the bone itself and therefore unique. The texture is made prominent after the basic shape is formed in the bone, but before the metal is cast. The rectangle was cast in one piece and so required a large bone. Cuttlefish bone is a good insulant allowing the silver to stay molten long enough to penetrate the relative long narrow channels by gravity.