Supply and demand for everything ultimately determines relative value. If necessary to prop up deflating bank asset values, central banks will print endless supplies of paper money whereas gold, silver, diamonds and other hard assets will remain scarce and tend to far out-value what streams from the printing presses over time. Every fiat currency over thousands of years has failed. The economic laws have not been repealed as digital fiat has replaced paper fiat.
Central banks do not print money. They issue currency as a liability against assets of Treasury securities that they obtain from primary dealers. There is no "new" money created in this transaction.
New money is created any time a promissory note is signed. Shrinking debt and bankruptcy cause a decrease in the money supply - since all money is debt based.
People still think of precious metals the same as when money was not debt based - prior to 1600 in Europe.
There is nothing wrong with "fiat" currency - as long as the currency represents labor that has already been completed...instead of a claim on the future labor of others.