A French law of 1803 granted anyone who brought gold or silver to its mint the right to have it coined at a nominal charge in addition to the official rates of 200 francs per kilogram of 90% silver, or 3100 francs per kilogram of 90% fine gold. This effectively established a bimetallic standard at the rate which had been used for French coinage since 1785, i.e. a relative valuation of gold to silver of 15.5 to 1. In 1803 this ratio was close to the market rate, but for most of the next half century the market rate was above 15.5 to 1. As a consequence, silver powered the French economy and gold was exported. Then the Forty-Niners went to California and the resulting supply of gold reduced its value relative to silver. The market rate fell below 15.5 to 1, and remained below until 1866. Frenchmen responded by exporting silver to India and importing nearly two-fifths of the world's production of gold in the period from 1848 to 1870. Napoleon III introduced five franc gold coins which provided a substitute for the silver five franc coins which were hoarded, but still maintained the formal bimetallism implicit in the 1803 law.