Since 1968, the San Francisco Mint has specialized in the production of U.S. proof coins. Each double-struck, mirror-finish coin is individually processed using the most advanced minting technology. These Washington quarter proofs were issued only as part of the year's proof sets, therefore the only way to obtain them was to break up existing sets. Most proof set owners are reluctant to do this, so individual quarter proofs are far scarcer than mintage numbers would suggest. This 31-coin set includes the special 1976-S Bicentennial issues; one clad and one struck with 40% silver content. It does not include the 1979-S Type II issue.