Proof coins are struck by technicians who hand feed the blanks into special presses. They are produced, examined and packaged using extreme quality control. It is very unusual to find major proof errors. A few broadstrikes, off-centers, double strikes (in collar) and off-metals have been known to be found in sealed proof sets. Proof errors are aggressively sought after by many error collectors.
A very small group of Proof errors recently came from a collection that was auctioned by the State of California. The U.S. Secret Service inspected and released this collection to the State of California determining that it was legal to own. The State of California then auctioned the collection and it has been dispersed since the sale.
Proof Washington Quarters struck in 1970 by the San Francisco Mint were clad. The first coin of this unique pair, a 1970-S Proof Quarter was over-struck on a Silver Barber Quarter and is one of two known. This mint error was originally discovered in group of San Francisco Proof Errors that was auctioned by the State of California. There is some detail on both sides showing the design of the Barber Quarter. This is one of the most famous U.S. Proof Major Mint Error ever released from the San Francisco Mint.
The second coin of this unique pair is a 1970-S Proof Quarter from the United States that was over struck on a 1941 Quarter from Canada. This unique mint error was originally discovered in group of San Francisco Proof Errors that was auctioned by the State of California. There is a significant amount of detail on both sides showing the design of the Canadian Quarter. This is one of the most fascinating and intriguing proof mint errors ever discovered.
These famous and enigmatic Washington Quarters from the San Francisco Mint struck in Proof, over a U.S. Silver Barber Quarter (1892-1916) and over a 1941 Canada Silver Quarter. These were both featured in a TV interview I did with Fox News. These fascinating errors went "viral" and were featured in USA Today, London's Daily Mail, AP News, Coin Week, New York Post, Newsmax, NBC News, Numismatic News, Time Magazine and on Maria Bartiromo's TV show.
Proof Errors are featured in the NLG award
winning book, World's Greatest Mint Errors.