An abrasive is a substance that you use to smooth out or mould or finish other softer materials through extensive rubbing. They work by scratching away surfaces of materials to get rid of unwanted substances and roughness. Some of the conventional abrasives include sandpaper, emery, sand and pumice. These different types of abrasives are used to smooth rough surfaces before applying paint or polish. They also help in adding shine to metals like gold, silver or platinum.