I'm not certain that was a great title but I really need expert help! I'd like a single tiny diamond on a 16 in or 18 in chain. Tiffanys grades diamonds over .18 . My local family business jeweler does not. If I were to purchase a .21 stone on a platinum chain from Tiffanys , the price would be in the low $2,000s. But from local jeweler , same size stone on a white gold chain costs $460. For a diamond that small, please advise if better to get the Tiffany branded one. Platinum or white gold chain doesn't matter to me. Thanks!