The procedures the U.S. Mint follows to prepare the dies used to
strike the Enhanced Uncirculated 2013-W American Eagle silver dollars
are part of an extensive process. Multiple operations must be executed
to create the desired final finishes found on the coin.
The Enhanced Uncirculated coin accompanies a Reverse Proof coin in
the 2013 American Eagle West Point Two-Coin Silver set.
Working dies for the West Point Mint are fabricated at the main
Philadelphia Mint, then shipped to the West Point facility where they
receive the final finishing steps, which involve polishing and
generating different intensities of laser frosting.
The production process for the dies can be separated into five stages.
Stage 1 produces the raw working dies as they are received at the
West Point Mint from the Philadelphia Mint.
For Stage 2, the entire face of the obverse or reverse die is
subjected to manual and automated horse hair brushing as a preliminary
polishing and cleaning step. The manual polishing is completed first
to get the difficult details, and then the automated polishing is used
to give all areas a consistent finish, according to Mint officials.
Manual polishing achieves a consistent finish in the areas that are
harder for the auto polisher to reach, Mint officials state.
When manual horse hair brushing is used, only one die is brushed
at a time. The system used for auto brushing allows up to 10 dies to
be installed in a rotating carousel. The automated horsehair brush
process creates a reflective surface of artwork elements.
For Stage 3, the fields on the Enhanced Uncirculated 2013-W
American Eagle’s obverse and reverse are given their light frosted finish.
Each side will also have two other finishes, generated in Stage 4.
At Stage 4, on the obverse of the coin, a brilliant polished finish is
executed on the mountains, what would be the red stripes and blue
field of the U.S. flag, the date and Liberty’s sandals. The remaining
elements and lettering on the obverse are given the standard heavy
frosted finish. Also during Stage 4, on the reverse, the ribbon in the
eagle’s beak, the arrows and the oak branch are given a brilliant
polished finish. The lettering and other design elements on the
reverse are given the heavy frosted finish. Also, the border and
stripes on the shield are polished.
The Stage 5 steps involve ultrasonic cleaning and physical vapor
deposition ceramic coating.
Trays of dies from Stage 4 traverse through a series of ultrasonic
cleaning stations before being dried and readied for the PVD step.
Bill Giraud, supervisory engraving engineer at the West Point Mint,
says the ultrasonic cleaning removes any oxide layers that have built
up on the face of each die during the laser frosting execution. Giraud
said the dies need to be perfectly clean for the thin layer of chrome
nitride to properly adhere to the die face during the PVD procedure in
PVD is a process that involves evaporation and deposition of a
material. A thin chrome nitride film is applied by the Mint through
the PVD technique known as “sputtering” within a high-intensity
magnetic field. The film helps to protect the dies during striking, by
adding lubricity that reduces friction that could cause die
degradation, according to Mint officials.
The PVD process is more environmentally safe than the hexovalent
chrome process once used by the Mint, according to the Mint.
The layer of chrome nitride doubles the die life, Giraud says.
The finished dies for the Enhanced Uncirculated coins are
installed vertically on Gräbener GMP 360 presses. The hammer die
imprints the obverse and the anvil die the reverse.
The Enhanced Uncirculated coins are struck three times on
specially burnished planchets, with a striking pressure of 210 metric
tons per strike to bring up design details. Before striking, the
planchets for the coin are burnished using steel shot, soap and water. ■