Immediately after President John F. Kennedy was assassinated, plans were made to honor him on the half dollar. Engravers Gilroy Roberts and Frank Gasparro created an impressive design that remains extremely popular with collectors today. Ninety percent pure silver coins were struck in 1964 only; from 1965 to 1970, the half dollars contained 40 percent silver, and thereafter they were made of a sandwich of pure copper between layers of copper-nickel. All dates are common.