More than a dozen different forms of design doubling have been
defined, with none more confusing than “flat field doubling.”
Assumptions about the nature and origin of flat field doubling
vary considerably, and examples used to illustrate this form of
doubling are not entirely consistent in appearance.
Photographs of two cases of flat field doubling have been provided
by Jason Cuvelier. They consist of the Mint mark of a Proof 1984-S
Lincoln cent and several obverse design elements on a Proof 1985-S cent.
Alan Herbert coined the term and established the original
definition, though certain assumptions in the definition may need to
be rethought. On page 275 of the Official Price Guide to Mint Errors
(6th edition), Herbert defines flat field doubling as “A coin (usually
a proof) which was struck normally and was struck a second time while
still in the collar, with die bounce or chatter damaging the design
after the first strike, the second strike driving the displaced metal
into the field, showing on the struck coin as a hazy, greatly
enlarged, and irregular outline of the design element on the surface
of the surrounding field.”
Herbert is suggesting that flat field doubling is a form of close
double strike. The final phase of the first strike leaves the coin
with marginal shelving characteristic of a form of machine doubling
Herbert designates as “push doubling.”
A severe case of push doubling is shown here in a 1991 Lincoln
cent. Right after the obverse (hammer) die reached the lowest point of
its downstroke, it bounced up, shifted to the left, and landed lightly
on the newly-struck design, creating a broad shelf along the right
side of Lincoln’s face.
The next step in Herbert’s scenario has the hammer die retracting
in the same position it occupied during the light touchdown that
created the marginal shelving. The process is completed by the second
strike, when the hammer die crushes the shelves down to the level of
Both machine doubling and flat field doubling are usually
restricted to one face, and the face affected is usually the one
struck by the obverse (hammer) die. It therefore seems safe to assume
that flat field doubling is a form of “one-sided” or “obverse-only”
double strike. In this form of double strike, it is the die that
shifts position, not the planchet. An unstable die or die assembly
underlies all forms of machine doubling and all one-sided double strikes.
However, I suggest that machine doubling is irrelevant to the
formation of flat field doubling. Under the elevated pressures used to
strike Proof coins, a second strike delivered by a shifted hammer die
would crush flat the margins of any elements overlapped by the field
portion of the die. This being the case, flat field doubling is
reduced to nothing more than a close, one-sided double strike.
Should we therefore simply call all such errors one-sided double
strikes? Probably not, since all Proof coins are struck at least twice
and calling attention to that fact is redundant. Instead we might
consider adopting the term “imperfectly aligned Proof strikes” as a
substitute for “flat field doubling.”
Flat field doubling can be widespread or it can be quite
localized. On the 1985-S Lincoln cent referred to earlier, flat field
doubling affects many obverse design elements, including the date,
Mint mark, LIBERTY and IN GOD WE TRUST. When doubling is localized, it
is usually found near the coin’s periphery. Such localized doubling is
probably caused by a slight pivot of the hammer die assembly.
It should be remembered that Proof coins are subject to ordinary
machine doubling on the final strike. In some cases this is mistaken
for flat field doubling. Shown here is a Proof 1962 Jefferson 5-cent
coin with strong doubling on the last three digits of the date. It’s
evident that this is push doubling rather than flat field doubling
because a slightly elevated shelf extends from the right side of each
affected numeral and the uncrushed portion of each numeral is
abnormally thin. Since the doubling is localized at the periphery it’s
likely that, during the bounce, the die assembly pivoted around an
axis located well to one side of the die’s central axis.
Flat field doubling adds only a slight premium to the value of a
Proof coin. However, if there is complete separation between the
flattened elements and their normal raised counterparts, value skyrockets.
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 firstname.lastname@example.org or to
800-673-8311, Ext. 172.