The hubbing process, while
rather simple in its procedure, is rather complex in the varieties
that it produces. Once the master die (incuse image) is created
(see previous article for an explanation), it is used to hub or
squeeze a working hub (relief image), which is in turn used to hub a
working die (incuse image). Since one hubbing is not usually enough
to bring up a sharp image, the die is annealed (softened by heat)
and re-hubbed, occasionally multiple times. If the working hub and
working die with its initial image are not fitted together properly
in the press, a doubled image occurs on the die. This doubled die
will in turn transfer a doubled image to every coin it produces.
While much has been made of the way in which a doubled die is
produced (the complex part), the important thing is to be able to
recognize the characteristics of hub doubling. These
characteristics include raised, rounded images with splits in the
serifs and valleys or furrows between the images. These are the
same characteristics as found on repunched dates and repunched
mintmarks. Being able to distinguish hub doubling from �machine
damage doubling� (sometimes called �ejection doubling,� �mechanical
doubling,� or �strike doubling�) is a mark of the advanced variety
collector. However, anyone can learn the difference if they are
willing to take the time to study the photos and the coins.
In its infancy, the collecting
of hub doubled coins, commonly known as �doubled dies,� centered
around the circumstances that produced the various kinds of doubling
known. For example, the doubling on some coins appeared all the way
around the rim lettering in a clockwise or counter-clockwise
fashion. Other coins exhibited doubling on just some of the rim
lettering. On other coins, the doubling was directed toward the
center or the rim. Still on others the doubling affected only
certain design elements. Thus the following classes of hub doubling
were proposed, principally by Alan Herbert, to explain these
differences. Most hub doubling is now regarded as a hybrid of these
classes. It is very difficult with only a coin in hand to logically
backtrack and find the cause of its hub doubling. So many things
can and do happen in the hubbing process that figuring out exactly
what happened in each case may not be possible. Again, the
important thing is recognizing the variety as true hub doubling, not
in determining to which class of hub doubling it belongs.