Aluminium
A precious metal that became common was aluminium. Although aluminium is one of the most commonly occurring elements in the Earth's crust, it was at one time found to be exceedingly difficult to extract from its various ores. This made the little available pure aluminium, which had been refined at great expense, more valuable than gold. Bars of aluminium were exhibited alongside the French crown jewels at the Exposition Universelle of 1855, and Napoleon III's most important guests were given aluminium cutlery, while those less worthy dined with mere silver. Additionally, the pyramidal top to the Washington Monument is made of 100 ounces of pure aluminium. At the time of the monument's construction, aluminium was as expensive as silver. Over time, however, the price of the metal has dropped; the invention of the Hall-Héroult process in 1886 caused the high price of aluminium to collapse permanently.
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