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Mint Error Coins
Every coin series has it's failures. These are
known as errors or mis struck coins, and have a following all their own.
(Although freshly minted coins are carefully screened at the Mint, some errors
manage to escape the process and land in mint-sewn bags, later to be sent to
banks.) Both their scarcity and novelty attract new error coin collectors every
year. There are many different errors in processing and striking, but only the
major types will be covered here. For the benefit of clarity, you can click on
the examples to view enlargements.
Normal Operation:
Under normal circumstances, the striking process
involves the introduction of coin "blanks" into the coin press, where
they are struck, then ejected after hopefully make a good impression. (Insecure,
the whole lot.) This is almost always the case, but, alas, the products of man
are not always perfect.
Blank Planchet
 Our first example is a blank planchet, or coin
blank. (Blank planchet is easier understood than a blank blank. Besides, you
might think I'm cursing.) There are two types: one which has been freshly cut in
the blanking press (Type One), and one which has slightly raised rims after
going through a softening process (Type Two). They simply slipped by the
striking presses (probably couldn't stand the pressure, anyway). These are the
most common type of error, with blank pennies trading among dealers for around
10¢ apiece.
Clipped Planchet
 The clipped planchet error occurs during the
stamping process, where thin sheets of metal are fed into a stamping machine
that punches out rows of coin blanks. If the sheet shifts (don't say that too
fast) during the process, blanks may have sections missing where previous blanks
have been removed (see illustration), creating a curved clip. A straight clip,
on the other hand, comes from an incomplete stamping along the edge. This is
another relatively common error.
Off Center Striking
 One of the more dramatic errors, the off center
strike happens, as the animation illustrates, when a coin blank is mis-fed into
the coin press and only part of the planchet is struck. Each error is different,
and is categorized by two different measurements: The amount of the coin design
that is visible (i.e., 25% off center), and where the off center design is
located in reference to a clock. (The coin pictured would be off center at 2:00.
I tend to wait until happy hour.) Some collectors make clocks with an
appropriate off center coin at each hour on the dial face.
Double Striking
 The double or multiple striking error can be the
result from several situations. As the illustration shows, a double strike can
occur from one die. However, the Mint utilizes two to four dies in close
proximity to increase production. A multiple strike could also happen when a
coin is struck, then bounces from table vibration into the path of another die.
At press speed of two strikes per second, this is a possibility, as are other
scenarios. This error is the most popular among collectors and the biggest
attention getter.
Broad strike
 Not to be confused with marital abuse, this error
type occurs when dirt or debris lodge between the plate collar and the lower
die, inhibiting its movement. If the die is stuck in the up position as shown in
the animation, the planchet will spread into a bowl-like object when struck. If
the entire design is visible on the error, it is considered a broad strike. If,
however, any part of the design is missing due to the coin not being centered
under the die, then it's considered to be an off center error. This mis strike
does not share the same level of popularity as other errors, but is still an
important error type.
Valuation
Prices of error coins vary considerably, and are
based on denomination, date (if the date is visible), how significant the error,
error type, how scarce the error is, and the dealer's demeanor. Usually the
lower denominations (cents, nickels) are the least expensive.
The most common type, blank cent planchets, can
be had for as little as a few dollars, whereas the illustrated double struck
nickel would be around US $35~$45. Be aware that values of error coins have been
stable and steady over the decades. This is not an investment hobby, but an
enjoyable and educational experience, and a good illustration of our imperfect
world.
For
more Help check out these others definitions
Reference: The Error Coin Encyclopedia, Second
Edition, Arnold Margolis, 1994
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