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
Shagreen Shagreen became fashionable again, partly due to the renewed interest in the Art-deco period. A range of items, including furniture such as small tables, have been manufactured since then, providing work for a small number of craftspeople catering to the luxury market. Small decorative items made of shagreen and silver have become popular in Southeast Asia; most are manufactured by high-end design studios in Thailand. In medicine, a shagreen patch is a patch of shagreen-like rough skin, often on the lower back, found in some people with the genetic condition tuberous sclerosis. Shagreen Shagreen is a type of rawhide consisting