PART VI. Striking Errors:
Obverse Die Cap (Hammer Die Cap in most years)
Definition: This error develops when a newly-struck
coin adheres to the hammer die. The
hammer, or top die, functioned as the obverse die through most of the Mint’s history,
with the exception of such issues as the Winged Liberty or “Mercury” dime and
the Indian Head or “Buffalo” nickel.
Beginning in 1992, there was a gradual changeover to a setup in which
the reverse die functioned as the hammer die.
However, most or all hammer die caps from this year on were still
produced in presses in which the obverse die was the hammer die. Therefore, it is perfectly acceptable to
refer to these errors as obverse die caps.
Almost all obverse die caps
are struck out-of-collar and take the form of cup.
The reverse or working face
of the die cap can carry a normal, raised reverse design. Such a cap will leave a brockage on each
planchet it strikes.
Some obverse die caps carry
a brockage of the obverse design on the working face. Such a cap will leave a counterbrockage on
each planchet it strikes.
Still other obverse die
caps have no design at all on the working face.
These “uniface die caps” strike coins that carry no design on their
Theoretically, any sort of
error coin can stick to a die and form a cap.
Thus the kinds of designs left on the planchets struck by a cap can be
quite diverse and complex.
Regardless of what design
(if any) it carries, the working face will eventually be worn smooth from
striking a succession of planchets.
Thereafter the cap will only strike generic capped die strikes with no
design on the obverse face except a raised ghost of the obverse design that bleeds through
the thin floor of the cap.