U.S. Mint treatments on Reverse Proof set coin dies
- Published: Nov 21, 2018, 3 PM
Dies used to strike the 2018-S Kennedy half dollar in the San Francisco Mint 2018 Silver Reverse Proof set received a surface treatment completely different from the remaining nine coins in the limited-edition set, although the treatments resulted in all the coins having the same basic appearance.
Inside Coin World: Counterfeit Trade dollar with wrong reverse: In the Dec. 10 issue, columns exclusive to subscribers include one on a counterfeit Trade dollar with the wrong reverse and a spotlight on Wisconsin quarter varieties.
The set contains a Lincoln copper-plated cent, Jefferson copper-nickel 5-cent coin, Jim Thorpe, Native American manganese-brass clad dollar, and .900 fine silver Roosevelt dime, Kennedy half dollar and five America the Beautiful quarter dollars, reflecting Pictured Rocks National Lakeshore, Apostle Islands National Lakeshore, Voyageurs National Park, Cumberland Island National Seashore, and Block Island National Wildlife Refuge.
Dies to strike each of the coins in the set are subjected to a combination of polishing and laser frosting operations that are executed mechanically or manually. On the dies, all of the devices to be raised on the finished coin are recessed.
On the Reverse Proof 2018-S Kennedy silver half dollar, a heavy frosted finish was imparted on the obverse and reverse fields, shown in blue on the color graphic. The obverse areas shown in purple, Kennedy’s portrait and the rim, received a light plus finish; a light finish, represented in lime green, was applied on the date, Mint mark, LIBERTY and IN GOD WE TRUST.
On the reverse, a light finish was executed on UNITED STATES OF AMERICA, HALF DOLLAR and the 50 stars encircling the eagle. The eagle, olive branch, arrows, ribbon inscribed E PLURIBUS UNUM, rays, clouds and stars above the eagle received a light plus treatment.
To achieve these results, portions of the die’s design area were masked off by computer-generated templates. Each part of the design to be treated received a laser treatment executed at different levels of intensity, providing varying aesthetic results.
The other Reverse Proof coins in the set (all of the denominations except the half dollar) received a mirror polish on the main design, inscriptions, date and Mint mark, a standard laser-frosted finish on the fields and a light laser frosting treatment on the rim.
On standard Proof coins, raised elements, such as the portrait or main design, inscriptions, date and Mint mark, are frosted, while the fields are polished to the mirror effect.
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