Hello, in answer to your question over on the blogs section, US coins were 90% silver up until 1964, after coins dated 1964 from 1965 and up coins were made with an alloy of copper and nickel, sometimes called a clad coin, (also called a Johnson sandwich). Kennedy half dollars were made with an alloy containing 40% silver until 1970, the reason for the change was that inflation had caused the cost of the metal to exceed the face value of the coin, it made no sense for the mint to lose money on every coin they made.
