Watershed Dates in the
Modern Minting Process

1909 – The beginning of the modern minting process is set in 1909. Prior to 1909 a partial hubbing process was utilized by the U.S. Mint. This process left the date and mintmark to be hand punched into each working die. 1909 saw for the first time, the date engraved into the master die, so that every working hub and working die carried the same date positioning. Mintmarks, however, were still applied to the working dies by hand as each branch mint had a need for dies.

1985 – The U.S. Mint began engraving the mintmark into the master die for all proof coinage. The last year possible for an RPM on a proof coin is 1984, however, the last known RPM for proof coins is 1975. In the middle of 1974 the S mintmark punch broke and a new punch with a different style of S was placed into use. This new punch was really an old punch first used in 1941-1952. The punch began to deteriorate rather rapidly producing deterioration doubling and finally deteriorating into a blob so that it too had to be replaced in 1979.

1986 – The U.S. Mint began experimenting with a single squeeze hubbing process. This process eliminates the need to anneal a die and then re-hub it in order to get the proper depth for striking coins.

1990 – The U.S. Mint began engraving the mintmark into the master die for the cent and nickel denominations. The last year possible for an RPM on a business strike cent or nickel is 1989. There are several known RPMs for the 1989-D cent and a couple for 1989-D nickel.

1991 – The U.S. Mint began engraving the mintmark into the master die for the dime, quarter, and half dollar denominations. The last year possible for an RPM on a business strike dime, quarter or half is 1990. The last known RPM for a dime is 1988-D. The last known RPM for a quarter is 1989-D. The last known RPM for a half dollar is 1989-D and can be found in Mint Sets.

1996 – The Denver Mint opened its own die shop and began using a single squeeze hubbing process for cents through quarters. Thus most doubled die classes were effectively eliminated. There are a couple of ways for doubling to occur on the die during the single squeeze process, but the vast majority of doubled dies are now a thing of the past. There are some 1996 dated doubled die obverses on the Philadelphia cent, which used the multiple hubbing process.

1997 – The Philadelphia Mint began using the new single squeeze hubbing process for cents through quarters.

1999 – The U.S. Mint adds the half dollar to the single squeeze hubbing process. The last known doubled die for the half dollar is on the reverse and dated 1994-S.

1999 – The U.S. Mint used the old hubbing equipment to create the SBA dollar coins needed late in the year and for collector proof sets. A couple of nice doubled die obverses are known for the 1999-P proof SBA.