While sitting in my office the other day, a fellow from another company which
is housed in the same office building stopped by to chat.  After about five
minutes of talking about the beautiful weather we are having here in Minnesota,
he reached into his pocket and pulled out some coins, looked at them, then
announced he was a quarter short and asked if I could lend him a quarter for the
soft drink machine.  "Sure!"  I told him.  Reaching into my
pocket, I felt I had nothing but quarters, so I pulled one out and flipped it to
him, and off he went.  About thirty seconds later, he returned.  "What
kind of a quarter is this?" he asked.  Well, it seems I gave him a nickel
struck on a quarter coin blank. An error coin!  All of us utilize coins day
after day without a second thought.  It is through the study of coin errors
that we gain a grater appreciation for the manufacturing process, and just what
goes into the production of the coins we use every day.

Every type of error coin has a name.  We as Coin Collectors are aware of
the existence of error coins on a limited basis, for example the 1955 double
die
Lincoln Cent.  How was that coin made?  The press double cycled, and
with a slight movement of the coin in the press, we get a coin that looks out of
focus or blurred.  There are collectors who would gladly pay $1000.00 for a
nice uncirculated example of that coin for their collection.  Let us take a
look at just some of the error coins on the market today, and look at just how
errors like this could occur.  Soon, you will gain a greater appreciation
of exactly what goes into the process of supplying our coinage.

One of the more dramatic error coins is called the clipped planchet. 
As we all know, a planchet is a coin blank.  Strips of coin metal stock are
fed through a machine called a Blanking Press.  This machine punches out
the coin blanks from the metal strips.  It punches blanks or planchets,
indexes or moves the metal strip to the next position, punches planchets, and
indexes again, and so on.  Occasionally, that index function doesn't work
properly, and you have coin blanks with a piece clipped out of them. 
Somehow, they end up being struck into coins, quality control misses a few of
them, and you have an error coin in circulation.

A broadstrike is another fairly dramatic error coin.  When a
planchet is fed into a press for striking, it sits in a collar.  It is the
collar that holds the coin's shape, and places the reeding (grooves) around the
edge of the coin.  Most likely during the set-up period, and during the die
alignment period, the collar is removed.  A coin struck without the collar
present will expand in size, or squish out from under the striking dies. 
So the coin will be larger then it should, and missing any edge design.

An Off Center Strike is another fairly odd looking error coin. 
As the coin is automatically fed into the press, it doesn't seat into the collar
correctly, and the coin is struck.  Part of the impression is on the coin,
and part of it is not.  These Off Center Strike errors are rated by
the percentage they are off center.  The further off center the design is,
the more expensive the coin (the grade of the coin is also a factor to
consider).  With all things being equal, an impression that is 15% off
center will generally have a greater value then a coin that is 5% off center.

The Mated Pair is one of my favorites, and one that is seldom seen. 
This error occurs when two planchets feed into the press at the same time, and
they are either overlapping or abutting.  The press strikes once, and the
coin design is shared by both planchets, with the planchets being fused together
from the pressure and the heat created from the strike.

Some of the error coins that have surfaced are almost beyond imagination as
to how they could possibly come to be.

The Double Denomination is certainly an interesting coin.  This
occurs when a previously struck coin, ends up being fed through the press that
is striking a coin of a different denomination.  Does that mean, if a
Lincoln Cent is struck onto a previously struck Jefferson nickel, then that new
coin is worth 6¢?  It is fun to make a joke,
but it does make one wonder, just how did that happen?

The Mule is another error coin that seems
to make one wonder.  The Mule is one of the most cherished of all
error coins.  It is a coin created by a mismatched combination of dies. 
In other words, dies of different denominations not meant to be paired, e.g. the
reverse of the coin is that of a Washington Quarter, and the obverse is a
Jefferson Nickel.

Other types of error coins are known as: a
Brockage, Clashed Dies, Cuds, Die Chips & Cracks,
Multiple Strikes, Dropped Letters, Fold Strikes, Edge
Strikes, Indents, Laminated Planchets and Misaligned Dies,
just to name a few.  These errors can be found even though the U.S. Mint
has a fairly efficient Quality Control Department, and this is why.  In
1999, for example, the Philadelphia Branch of the U.S. Mint manufactured
10,877,624,000 regular issue U.S. coins.  That number does not include the
commemorative coins, or the coins made for foreign governments.  The Mint's
Inspection Department cannot find all the errors with that many coins to inspect
in one year.  Some will get through to the general public.  You
can bet on it.

There is one more error coin I would like to address, and that is the double
headed or double tailed coin.  It is next to impossible to have a real one
of these coins, and there has only been one documented case of a real double
tailed quarter in existence.  Let me explain why.  At the U.S. Mint, a
coin press is made of two dies.  The die for the reverse side of a coin is
called an anvil die.  It is a stationary die that does not move.  The
obverse die is called a hammer die, and that is the part in the press that moves
up and down with a force in excess of 37 tons per square inch (minimal pressure
to strike a one cent coin).  The anvil die will not fit in the hammer die's
position, just as the hammer die will not fit in the anvil die's position. 
For those of you who are following this closely, you can see the law of
probability against a double headed or double tailed coin mounting up quickly. 
You would have a better chance of winning the "Powerball Lottery" several times
over before you would have a double sided coin struck, let alone it passing
through inspection.  If you have a double headed or double tailed coin, and
you want to make sure it is real, there are several tests you can do before you
send it to a third party grading service for authentication.  First, take
measurements.  Make sure the diameter, thickness and weight meet all the
specifications for that particular denomination, and type of coin.  Second,
examine the edge of the coin under high magnification.  You are looking for
a seam where two halves could have been fused together.  A real coin
will not have a seam.  Third, do the "ring test."  Find a normal
coin of the same date, denomination and design. Drop them both on a table or a
counter top.  If the ring sound is the same, then it is possible that the
double sided coin is real.  If the ring sound is different, then the double
sided coin is not real.  If your coin passes all three tests, then send it
in to a third party grading service to be graded and certified.  You just
may own the second double sided coin in the history of the U.S. Mint.

Error coins are fun, and they give one a great appreciation of the process of
manufacturing coins.  It is through the study of error coins that a
collector will learn about: the alloys used in coins; planchet preparation; how
the dies are made; and, the process of striking coins, as well as, just what can
go wrong throughout the whole process.  It is through this process of
learning that one gains a greater appreciation for their hobby of Coin
Collecting.