The mint envelope was never opened. It hasn’t seen the light of day since it was sealed in 1970. Very last set ever with a silver coin. Check out my other auctions. Priority is also an option for you to choose but you have to change it. Thanks for looking and add me to your favorite sellers to get notified when I list more new used custom items. The 1970 US Mint Proof Set is a collection of uncirculated silver coins struck with a high degree of finish at the San Francisco Mint. These coins are guaranteed by the U. Mint and have a fineness of 40%. The set includes coins from the United States with no modifications, making it a valuable addition to any coin collector’s portfolio.