Aluminum was valuable because it was exceedingly difficult to extract from ore, but in 1886, with invention of the Hall-Héroult process, its supply exploded and its price fell through the floor. An equivalent explosion in the supply of other precious metals is unlikely, but industrial demand for precious metals is unreliable. Much of the platinum and palladium presently sold is bought by the motor industry. It uses the metals to make catalytic convertors, but is hunting for a way around its dependence on such scarce resources. Demand for silver declined with the rise of digital photography, because the metal was an important part of developing film. Technological advances like these can't be predicted, but they can easily make a fool out of investors hanging onto metals they think are worth more than gold.
