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
Horween Leather Company the Horween family that has worked in the company: About 85% of the leather at Horween Leather Company is made from cowhide. The company's workers take raw hides, which arrive salted to prevent deterioration, trim them, and remove their hair with chemicals in an extremely large washing drum. The leather is then treated with salt and pickled for 24 hours, so that it reaches a desired pH level. It is then bated, tanned, and finished. Horween Leather Company produces many different full grain and corrected grain leathers. Its leather is used in a number of products including footwear, sports equipment,