 Despite not having a sting , the porcupine ray is capable of injuring humans with its many sharp thorns . It is reportedly bold and tolerant of being approached closely underwater . The tough , thorny skin of this ray , made into a form of leather called shagreen , had many historical uses . In particular , it was used to cover the hilts of various melee weapons , as its extremely rough texture prevented slippage during battle . For example , the Japanese deemed it the only species whose skin was acceptable for covering sword grips . The Malayans used it to cover shields . The skin was also used ornamentally , such as by the Chinese , who dyed it and ground down the thorns to yield a mottled pattern . The native inhabitants of Funafuti Atoll used dried portions of the ray 's tail as a rasp @-@ like tool . 
