The Silver Proof Set adds the luster of 90% silver. These coins are distinguished by their brilliant finish that is achieved by striking the coins twice, for a more defined relief, then buffing them to a high shine. Their frosted, sculpted foregrounds give them a special "cameo" effect, created by the exacting proof process. These "Proof" quality coins are only minted at the San Francisco mint. Beginning in 1936, the U.S. Mint began producing proof sets. Sets struck from 193642 and, when resumed, from 195072 include the cent, nickel, dime, quarter, and half dollar. From 1973 through 1981 the dollar was also included, and also since 2000. Proof Susan B. Anthony dollars were struck in 1999, but they were sold separately and not included in the proof sets in that year.