In recent years, Nancy Oliver and Richard Kelly have emerged as two of my favorite numismatic sleuths and authors.
Comprehensive Catalog and Encyclopedia of Morgan &
Peace Dollars by Leroy C. Van Allen and A. George Mallis. Though not
detailed, a person already familiar with the die-preparation process should be able
to make a fairly good interpretation.
In short, die radius refers to the curvature of the die face. Early United States
coins typically had flat fields as a consequence of the primitive method of die
preparation. Starting with the Christian Gobrecht designs of 1836-40, USA coinage
began to reveal a slight concavity to the fields, though this isn't always apparent
on casual inspection. Concave fields were the result of convex die faces, and this
slight curvature had to be applied in a step that was separate from the actual sinking
of the die. A working die that was ready for polishing was set into a jig with its
face upward. The face of the die was then brought into contact with a polishing
disc, or plate, that had a very shallow concavity to it. When spun against the face
of the die, the disc imparted the same curvature profile, but the result was convex.
The purpose for giving the die face a slight curvature was to facilitate the movement
of metal during the coin striking process. Experimentation with different degrees
of curvature would ultimately determine the best standard for filling the dies in
a single blow from the press. These experiments were carried out at the Philadelphia
Mint's Engraving Department with all new designs starting at least as early as the
Morgan dollar coinage of 1878 and possibly earlier. The difficulty that the Mint
experienced in producing a satisfactory number of coins from each die pair with
this coin type's original, high-relief obverse and its eight-tailfeather reverse
demonstrated the need for such trial and error before working dies were shipped
to all the branch mints.
Once the optimum die radius was determined in Philadelphia, duplicate radius plates
having this ideal curvature were sent along with the working dies to each of the
other mints, so that the process could be repeated on-site. It was necessary that
the various mints finished their dies locally, because the dies were sent from Philadelphia
in an unhardened state (hardened dies, if intercepted in shipment, could more easily
be used by counterfeiters).
If all went according to plan, the coins struck by each mint would be identical
throughout in their degree of definition. But, as any collector of uncirculated
Morgan dollars can attest, the sharpness of these coins varied considerably. This
variance occurred in a characteristic manner from one mint to another. For example,
New Orleans Mint Morgan dollars typically are soft at the centers and have strong
edge reeding, while those coined at Philadelphia have sharp central details and
mushy reeding. One can actually feel this difference by handling the coins' edges.
Clearly, the movement of metal was being directed in accordance with differences
in die radius.
The creation of radius plates went hand in hand with the practice of "basining,"
which I've described in previous columns. Basining was the process of giving dies
their face polish when being used for the first time. In fact, the term "basin"
often was used interchangeably by Mint employees to describe the face curvature,
or radius. Polishing of a die performed after its initial use to repair flaws or
to extend its useful life is not properly called basining, since the work was crude
and, it may be assumed, was done without a radius plate.
The new, sculpted designs submitted by outside artists beginning in 1907 gradually
rendered both radius plates and basining obsolete. The models as submitted already
included the desired curvature, though the Mint's own staff sometimes had to modify
this radius in the hub reduction stage.
David W. Lange's column USA Coin Album appears monthly in Numismatist, the official
publication of the American Numismatic Association