Monetization is the process of converting or establishing something into legal tender. It usually refers to the coining of currency or the printing of banknotes by central banks. Such commodities as gold, diamonds and emeralds generally do have intrinsic value based on their rarity or quality and thus provide a premium not associated with fiat currency unless that currency is "promissory". That is, the currency promises to deliver a given amount of a recognized commodity of a universally (globally) agreed-to rarity and value, providing the currency with the foundation of legitimacy or value. Though rarely the case with paper currency, even intrinsically relatively worthless items or commodities can be made into money, so long as they are difficult to make or acquire.