Before sandpaper was invented, people used shark skin, called shagreen, to smooth and polish wood
Photo source: Flickr
Due to the rough and abrasive properties of a dried up shark skin, also known as shagreen, before the invention of a sandpaper it was used to smooth and polish wood.
Shagreen is a type of leather or rawhide consisting of rough untanned skin, formerly made from a horse's back or that of an onager (wild ass), and typically dyed green. Shagreen is now commonly made of the skins of sharks and rays.
Shagreen has been used for other functions too. For example, Japanese warriors used shagreen on the handles of their swords to keep the swords from slipping out of their hands.