In 2010, the U.S. Mint began striking quarter dollars for its
America the Beautiful program. Each coin features a reverse design
that celebrates a national park or other site of national
significance. A raised perimeter ring on the reverse face houses an
array of incuse design elements.
The presence of these incuse elements raises the odds of seeing
new or unusual effects, even in so humble an error category as machine doubling.
Machine doubling occurs immediately after the hammer die has
reached the lowest point of its downstroke. It generally reflects
instability in the die, die assembly or the coinage press as a whole.
In some cases, either die can rebound from the surface of the
coin, shift laterally and land lightly on the newly struck design
elements. This produces marginal shelving at the edge of the design,
but can result in clear duplication of interior design details.
In other cases, a die simply shifts laterally after the hammer die
reaches its lowest point. This causes smearing of the newly-struck
design and the piling up of relocated metal into a series of ridges.
Raised and incused designs
While the same die motions affect both raised and incuse design
elements, the resulting appearance is rather different in the latter.
This has caused some cases of incuse machine doubling to be mistaken
for a doubled die (hub doubling), a mishap that results from multiple
impressions of a working hub into a working die. An example of
deceptive machine doubling in a 2010 Grand Canyon National park
5-ounce silver bullion coin was recently discussed by Ken Potter (http://numismaster.com/ta/numis/Article.jsp?ad=article&ArticleId=17345).
A commemorative quarter dollar recently found in pocket change by
Alex Tuel further illustrates the ease with which incuse machine
doubling can be mistaken for other sorts of minting errors and die
varieties. The coin in question is a 2011-D Olympic National Park
Tuel first presented his specimen on the message board of Lincoln
Cent Resource (www.lincolncentresource.net/forums/showthread.php?t=17470&page=3).
Photographs provided by Tuel showed a second set of overlapping
letters (E PLUR) that were offset and independent from their normal
counterparts. The extra letters are much thinner than the normal ones.
Early opinions gravitated toward a doubled die or a Type II
counterclash. The latter is a form of patterned die damage that
results when a hard piece of metal is struck twice (see Collectors’
Clearinghouse, Sept. 29, 2008).
I suspected machine doubling (as did others), but couldn’t be sure
just by looking at the photos. So I asked Alex to send me the coin and
he generously obliged. An examination under a microscope confirmed my suspicions.
The bottom (outer) portions of the letters E PLURIBUS show
conspicuous smearing, a sign of unwanted movement in the reverse
(hammer) die or hammer die assembly. The second set of letters was
evidently caused by a high bounce of the hammer die after it reached
the lowest point of its downstroke.
Forming incused letters
Remember that the incuse letters on the coin are created by raised
letters on the die face that extend well beyond the plane of the
surrounding field. In this series, the perimeter ring is recessed on
the die face and the letters stick up from its floor. The hammer die’s
bounce would have carried those raised letters completely out of the
recessed letters they’d just created. A slight shift to the northwest
positioned those raised letters directly above the raised perimeter
ring of the coin. Descending from the apex of its bounce, the hammer
die made light contact with the coin’s perimeter ring. This light
impact produced the second set of letters in the field. The reason
they’re so thin is that, in cross-section, the apex of each raised
letter is narrower than its base, and only the apex left an impression.
A high bounce with a strong lateral shift will sometimes generate
odd effects on coins with conventional raised designs. Previous
installments of Collectors’ Clearinghouse introduced the phenomenon of
“rim-restricted design duplication” (Feb. 22, 2010, Aug. 22, 2011).
This form of machine doubling leaves an entirely separate set of
raised design elements on the newly-formed design rim.
Coin World’s Collectors’ Clearinghouse department does
not accept coins or other items for examination without prior
permission from News Editor William T. Gibbs. Materials sent to
Clearinghouse without prior permission will be returned unexamined.
Please address all Clearinghouse inquiries to email@example.com or to
800-673-8311, Ext. 172.