The following is the Collectors' Clearinghouse column from the Dec.
19, 2016, issue of Coin World:
When the collar (the retaining ring that establishes the final
diameter of a newly-struck coin) experiences brittle failure, several
types of collar breaks (collar cuds) may result (Collectors’
Clearinghouse, Nov. 22, 2010).
A collar chip (chipped collar) occurs when a small piece detaches
from the collar’s working face.
A vertical collar crack involves no loss of metal, but does result
in a slight widening of the collar’s diameter. Single, paired, and
multiple collar cracks are known.
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A bilateral split collar occurs when two collar cracks at opposite
poles widen considerably, causing the collar to expand along one axis.
A retained collar break develops when the area between two collar
cracks sinks into surrounding softer steel or when the mobilized
portion of the collar is restrained by a surrounding clamp or bolts.
Retained collar breaks often measure 180 arc degrees, although smaller
examples are known.
An irregular collar break occurs when a substantial portion of the
upper margin of the collar’s working face breaks away. This breakage
can be spontaneous or can be caused by a collision with a misaligned
hammer die. An irregular collar break will display a ragged lower
margin where it meets the intact portion of the collar’s working face.
Finally, a full collar break entails the complete loss of the
collar’s working face along an arc that ranges from a few arc degrees
to well over 180 arc degrees.
Plain (smooth-faced) and reeded issues tend to develop different
types of collar breaks. For example, the presence of a tungsten
carbide steel liner in many plain collars may predispose these collars
to develop more irregular and more extensive forms of brittle failure.
The presence of ridges and valleys on the working face of reeded
collars presumably facilitates formation of vertical collar cracks and
related forms of brittle failure.
The defect that can only be found
on 2002-P Kennedy half dollars in modern era:
A collar break is expected to appear in the same spot on the edge
of every coin struck within that collar. The 2002-P half dollar
defies that expectation.
While die chips occur in both plain and reeded issues, their
location and etiology differ. In reeded issues they form when a part
or all of a ridge on the working face of the collar breaks off. In
plain collars they develop along the upper margin of the collar’s
working face. Shown in the second image in the slider above is the
edge of a 1982
Lincoln copper-alloy cent with two substantial collar chips.
Vertical collar cracks are known in both plain and reeded issues,
although I sense they’re more common in the latter. In reeded issues
the line of breakage is presumably guided and facilitated by the
vertically oriented valleys that form the reeding.
Bilateral split collars occur far more commonly among reeded issues,
like the 1967 Roosevelt dime shown in the third image
above. However, the widest example I’ve seen occurs in a 1964-D Jefferson 5-cent coin (see previous reference).
Retained collar breaks are similar in both appearance and etiology
to bilateral split collars. One way to tell them apart is to look at
the points of breakage. In a bilateral split collar, both points of
breakage will be marked by raised nibs. In a retained collar break,
there is usually a step at one or both ends testifying to a horizontal
shift or pivot of the mobilized segment. Nibs, when present, tend to
be rather small.
Retained collar breaks are much more common among reeded issues. An
exception exists among 1973-D Lincoln cents, where three different 180
degree retained collar breaks are known (see fourth photo above).
Irregular and full collar breaks are almost completely confined to
plain-edge issues (cents and 5-cent coins). This may be due to the
presence of a tungsten carbide steel liner. I suspect that this hard,
brittle alloy is both difficult to machine and vulnerable to breakage
should grooves be machined into its working face. Shown in the fifth
image above is a 1981
Lincoln cent with a 180 degree full collar break that extends
from 4:00 to 10:00.
The only reeded coin I know of with a full collar break is a 1998-D Washington quarter dollar shown in the
sixth image above in which the collar break extends from 1:30 to 5:30.
The coin also features catastrophic die damage on both faces and a
large corner die break (cud) on the obverse face (Collectors’
Clearinghouse, Oct. 27, 2014).
More on the U.S. Coins mentioned in this article:
Lincoln cent: The popular Lincoln
cent has gone through several reverse updates since it was
introduced in 1909 to honor the nation's 16th president on the 100th
anniversary of his birth. How much are Lincoln cents worth?
5-cent coin: If one word sums up the Jefferson 5-cent
coin, it would be "change" because throughout its history
it has endured many changes, from Mint marks and designer intitials,
to portraits of its namesake president. How much are
Jefferson 5-cent coins worth?
dime: Franklin Delano Roosevelt's sudden death of a
cerebral hemorrhage on April 12, 1945, compelled officials to
recommend the late president's portrait to be immediately placed on
a coin of regular issue. How much are
Roosevelt dimes worth?
quarter: The Washington quarter dollar, which has been
circulating since 1932, was born out of the Treasury Department's
desire to produce a coin to mark the bicentennial of the birth of
the first president of the United States. How much
are Washington quarters worth?