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
Santiniketan Leather Goods Santiniketan Leather Goods Santiniketan Leather Goods are leather products made in Santiniketan and surrounding villages near Kolkata, West Bengal, India. The material used is vegetable tanned leather with art work done by touch dyeing. Its artistic leather bags are popular in foreign markets and are exported to many countries including Japan and the U.S. They are generally made of E. I. Leather (East India Leather) from sheepskin and goatskin. This product has been registered for protection under the List of Geographical indications of the Trade Related Intellectual Property Rights (TRIPS) agreement. In July 2007, it was listed as "Santiniketan Leather