Although the coin has been minted for nearly eight decades, its visual design has changed very little. Most modifications were technical rather than aesthetic. In 1965, for instance, the coin’s composition shifted from 90 percent silver to a copper-nickel clad alloy under the Coinage Act of 1965, as rising silver prices made the earlier composition too costly to maintain. Around the same time in the 1960s, the mint mark, which had originally appeared on the reverse, was moved to the obverse beside Roosevelt’s portrait. Later, in 1980, the Philadelphia Mint began adding the “P” mint mark to the dimes it produced.