When people polish diamonds, they do so by rubbing them against a wheel that has diamond chips embedded in it. Such a proceedure should scratch the diamonds, not polish them. One team has figured out why it doesn't.
Diamonds aren't forever. They're one of the hardest materials on earth, but they get dirtied and chipped just like everything else on the planet. When diamonds are in a state of disrepair, or when they are brought up out of the earth as dull and uninteresting rocks, merchants and craftspeople get them shining by polishing them up.
The polishing process involves taking a diamond and putting it against a wheel. The wheel spins, polishing up the diamond to something gleaming and valuable. It seems as though this wheel should be covered with something fine-grained and soft. Instead it's covered by many jagged diamond chips. As most people who have worked with wood know, coarse polishing materials are necessary to take some of the more egregious scratches out of things, but as the polish becomes finer, finer materials need to be used. One doesn't polish a stained glass window with shards picked up from a construction site.
Recently scientists have looked into why grinding these diamonds against diamond fragments is such a good way to get them to gleam. They found out something interesting; the grinding builds up a film of diamond atoms. Any imperfections in the surface are plucked at by the diamonds in the wheel. When they come off the central gem, they form a soft layer of atoms around the diamond. Sometimes this layer is chipped away. Sometimes, the carbon atoms of the diamond are simply lifted away when they bond with oxygen atoms in the atmosphere. The diamonds are being air-cleaned.
Via Physics World.