Fish scale the surface, interacting only with the riblet tips, not causing any high-veloctiy flow in the valleys. Since this high velocity flow now only interacts with the riblet-tip, which is a very small surface area, the momentum transfer which causes drag is now much lower than before, thereby effectively reducing drag. Also, this reduces the cross-stream velocity fluctuations, which aids in momentum transfer too. The rough, sandpaper-like texture of shark and ray skin, coupled with its toughness, has led it to be valued as a source of rawhide leather, called shagreen. One of the many historical applications of shark shagreen was
The Shagreen Bone The Shagreen Bone The Shagreen Bone (, ) Op. 37-38 (1990) is a full-length ballet in three acts and an opera "entr’acte" in one act by Yuri Khanon, to a libretto by the composer based on Balzac’s 1831 novel "The Shagreen Skin". The ballet (Op.37) and the "entr’acte" (Op.38) were written in 1990 on commission from the Mikhaylovsky Theatre in Leningrad. The libretto is based entirely on the dialogues between the two characters – Pauline and Raphael. In 1992, an avant-garde film-opera "The Shagreen Bone" was shot at the Saint Petersburg Documentary Film Studio, with Yuri Khanon in the main