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
Chamois leather flesh split of sheepskin or lambskin, or from sheepskin or lambskin from which the grain (the top split) has been removed by frizing, and tanned by processes involving oxidation of marine oils in the skin." In the United States, the term "chamois" without any qualification is restricted to the flesh split of the sheep or lambskin tanned solely with oils (US Federal Standard CS99-1970). Chamois leather is often counterfeited with goat or pig skin, the practice of which is a particular profession called by the French "chamoiser". The term "chamois" as used to refer to specially-prepared leather originated sometime before