US Coins

Color charts designate laser frosting Proof polishing

Color-coded charts prepared and released by the U.S. Mint indicate the areas of Proof polishing and laser frosting executed on the dies for the Proof versions of the 2016 Mark Twain and National Park Service Centennial commemorative coins.

The 2016 Mark Twain program features Proof and Uncirculated versions of a gold $5 half eagle and silver dollar. The coins are scheduled to go on sale from the U.S. Mint at noon Eastern Time Jan. 14.

The 2016 National Park Service Centennial commemorative coin program offers Proof and Uncirculated versions of three coins — a $5 gold half eagle, silver dollar and copper-nickel clad half dollar. The National Park Service coins go on sale at noon Eastern Time March 24.

The Mint's color-coded graphics detail the design elements of the obverse and reverse of each of the Proof versions of the five commemorative coins from the two programs that are subjected to varying degrees of laser frosting, with the flat fields receiving Proof polishing resulting in mirrored surfaces. Some raised elements, usually lettering, may also receive the Proof polishing treatment.

Depending on the denomination and whether obverse or reverse, up to four different intensities of laser frosting may be employed on a single die — heavy, standard, light, and light-plus.

The heavy laser frosting is designated in blue; the standard frosting, in orange; the light frosting, in green; and the light-plus, in purple. Yellow is used to define the areas receiving Proof polishing.

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The Proof polishing is generally executed by automated means, but some finer details may be polished manually. Often, the complete face of the obverse or reverse die is subjected to automated Proof polishing, after which the die is moved to the laser frosting equipment. The areas to receive laser frosting are masked off through the use of a computer-programmed template that outlines the area or areas to receive the level of laser frosting desired.

Steve Antonucci, branch manager for Digital Development, Research & Development for the U.S. Mint at Philadelphia, explained the intensities of laser frosting as follows:

??Standard frosting is where the U.S. Mint started with its laser frosting parameters initially. This closely matched sand blasting. 

??Heavy frosting was developed to get the heaviest possible laser frosting for differentiation of certain details on a design. 

??Light frosting was later developed as part of our multi-tone frosting process to yield lighter highlights on the more subtle elements of a design. 

"On certain designs where frosting longevity is desired (die life), we developed and implemented light-plus," Antonucci said via email. "This gives a lighter frosting to specific design elements and helps to add visual interest to a coin."

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