The E-Sylum:  Volume 11, Number 8, February 24, 2008, Article 32

DICK JOHNSON ON MULTIPLE STRIKING FOR LARGE MEDALS

Dick Johnson writes: "Collector Tony Lopez had acquired a
double struck Edward Preble Medal (Julian NA-3) and was
asking questions about it.  Every collector should do this
-- learn as much as possible about items in their collections.
Tony wants to prepare an article on this medal. This week
he asked 'I am curious as to the minimum number of strikes
which can be attributed to creating this medal.'
Here was my reply:

”There is no fixed rule on the number of strikes for any
medal. There are so many factors involved --pressure of
the press, hardness of the metal blank, height of relief
in the die, thickness of the blank -- are the most
important factors in order.  A pressman will keep striking
a medal until he brings up all the relief in the die. (He
examines the high points like a collector does for condition.)

"But you must realize with each blow it WORK HARDENS the
struck metal. After perhaps one or two blows any further
striking would not move any more surface metal. Striking
freezes the molecules in a fixed position. The partially
struck medal must be RELIEVED by HEAT TREATING -- this
allows the molecules in the metal to break that fixed
position, to be able to move around again. This is called
ANNEALING.

"Iron has the amazing property that when heated and with
slow cooling, it REDUCES the hardness. Heating and rapid
cooling (like quick immersion into water, oil or molten
salt) HARDENS the iron. For this reason dies are always
made of iron. Items struck in metal have similar but their
own properties. Medals in bronze or silver, the most
common medal composition, are RELIEVED in a similar
heating and slow cooling manner.

"The relieved medal must be placed back on the press.
It must SEAT in the exact position of the previous blows,
the surface relief must line up exactly. For this reason
a pressman will usually place the die with the side of
greatest relief -- usually the obverse with a portrait
-- in the lower position in the press to aid in seating
the medal back in the press to be struck again.

"When a pressman is sloppy and does not seat the medal
exactly he will get a DOUBLE STRIKE with a double image.
You can easily observe both the relief from the latest
strike, and the UNDER RELIEF of the previous strike. If
he is really sloppy and places the partially-struck medal
back with the wrong side down, he will get the opposite
side's under relief. What you are calling a flip-over
strike. (When this happens in a coining press it is
called a flip-over double strike).

"In modern times large medals from one-eighth to one-fourth
inch thick (metalworkers measure thickness by GAUGE, in this
case gauge 3 to gauge 8) can usually be struck up in from
four to eight blows in a KNUCKLE-JOINT press of 1000-ton
pressure capacity. There are presses with lesser and greater
capacity and this will effect the number of blows. With
modern HYDRAULIC presses the pressure can be regulated and
this relief can be achieved with fewer impressions, say two
or three. Again, medals must be annealed between strikes
for either press.

"What press the medal maker will use depends upon what press
he has, or what press is available when the medal needs to
be struck. Once a medal die is made it can be used for either
press. You cannot tell by inspecting a struck piece whether
it was struck on a knuckle-joint press or a hydraulic press.

"Medal presses use only OPEN FACE DIES, called BOX DIES in
England. They are more suitable for large medals. (Dies for
coining presses are different -- not only does a coin die
have to be made to fit within its collar it must be compatible
with the housing of the press where the die is locked in
position.) Generally, open face medal dies can strike any
size up to 6-inch diameter. Generally, coining dies can
strike up to 2-inch diameter. However, in recent times the
industry has been pushing these limits upwards for both
methods.

"Your medal, made in 1806, was struck on a screw press.
All the conditions described above apply to items struck
on a screw press. The major difference: the screw press
was powered by man (horse, or water power). Modern presses
are powered by electric motors of course (since 1890)."

  Wayne Homren, Editor

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