Q. David Bowers
Introduction
In the course of reading the descriptions of specific commemorative coins in the present text, and in the process of collecting or investing in such pieces, you may find the technical and background information given in this chapter to be useful.
Models and Dies
In the course of discussing specific commemorative coins and various individuals quoted, I make reference to models, master dies, and other items in the coinage process. In connection therewith it is appropriate to mention here the sequence of operations from design to finished coin. ( Much of the following information was provided by Elizabethjones, chief sculptor-engraver of the Mint 1981-1990, and reflect U.S. Mint processes. Procedures used at private mints, mints of other countries, and other facilities are apt to differ in details.) The procedures involved have varied slightly over the years, and sometimes one or more steps are eliminated, but this is the basic concept used currently at the U.S. Mint:
(1) An artist creates a design concept and makes an appropriate sketch or drawing. Often during the creation of a commemorative coin several or even many sketches are made. These artistic concepts are studied, criticized, and in many instances revised.
(2) A sculptor (not necessarily the same artist who created the design) forms a three-dimensional version or model of the final sketch by sculpting (modeling) the features in plastilene (an oil-based clay) onto a plaster basin. The work is done in relief or in "positive" form. Models vary from about six to 12 inches in diameter, the most common being about eight to 10 inches. (At the Mint in 1990-1991 most models are in the six to eight inch range. The only 12-inch model in use is that of the Saint-Gaudens design for the U.S. gold bullion coins.) Separate models are made for the obverse and reverse.
(3) When the plastilene is modeled in as much detail as possible, for it is a fairly soft material (although it comes in soft, medium, and hard consistencies; each artist has his or her preferences), plaster is then poured over the model. It sets in an hour or slightly longer. This plaster is a mold, called a "negative." The new plaster negative is refined and worked on using fine metal tools, more detail is added, and letters are cut in (letters are always carved in the negative state). When this is done a separator is applied to the negative plaster, and more plaster is poured into and onto it. After the plaster sets, the new plaster and the old are opened up (released), thus creating a "positive" with the new plaster. From this point the artist can work on as many additional negatives and positives as desired, until he or she achieves as finely finished a model as possible.
(4) When the model is considered to be finished, a rubber mold is poured onto the final positive plaster, and is left to set or harden overnight. The next day the rubber mold (which is incuse or negative) is separated, and epoxy is poured into it. The epoxy "positive" image is then checked to see if it is perfect. (In yean; prior to 1982 a metal galvano, made by electroplating, was used at the Mint in place of the epoxy model. The electroplating process to create metal galvanos took approximately three days. Epoxy models hold up better on the Janvier machine, and show less wear after use. Corrections can be made on epoxy models by sanding, an easier process than the filing or hammering needed to correct a galvano.)
(5) The epoxy model is securely fastened onto a Janvier machine (reducing machine). A dulled point (called a stylus) traces the surface of the epoxy model, and by means of a pantograph procedure, causes a tiny rotating cutter to replicate a miniature version of the same design on the end of a steel cylinder, known as a master hub or reduction hub. Almost always the first cut on the Janvier machine is a "roughing cut," to cut away the excess steel of the hub. Then a second cut is taken, using a finer-tipped stylus at the tracing end and a sharper cutter at the cutting end. This is usually the "finishing cut." Sometimes, especially with a new and therefore untried design, there might occur a very fine texture on the surface of the hub, or perhaps fine concentric lines, requiring too much finishing by hand. In such an instance a third cut is taken, and usually achieves the desired result. Generally the smaller the diameter of the epoxy model, the better the cut, and the fewer cuts required. It is desirable to have all artists model their designs within strict specifications and to keep the relief low enough, yet detailed enough, so that the Janvier machine does not have to alter the relief to make it suitable for coinage. During the transfer process the relative relief of the epoxy model can be increased or decreased, according to requirements for coinage. Design features on the master hub are in relief.
(6) The master hub is hardened by a heat-treating process inside a furnace, followed immediately by a drastic change in temperature achieved by quenching in oil or brine. The exact method of heat treating used depends upon the type of steel used to make the die. The master hub design is then transferred by impact (actually a squeezing process under pressure of many tons in a press) to create a master die. The master die, in soft steel, is now subjected to a hardening process (this procedure is followed in subsequent transfer processes as well). Design features on the master die are incuse. In recent years, mintmarks such as P, D, S, or W, have been added by punching them in the master die. (The transition to punching mintmarks in the master die was made on various denominations duting 1990 and 1991. A slightly different procedure was used for the addition of mintmarks to Proof coin dies.)
(7) By applying pressure in a large hubbing press (slow squeezing), the features of the master die are transferred to a working hub. Design features on the working hub are in relief.
(8) By applying pressure in a large hubbing press (slow squeezing), the features of the working hub are transferred to a working die. Design features on the working die are incuse. Until recent years mintmarks were added by punching them on the working die. As multiple working dies were used, this accounts for numerous microscopic differences in mintmark placement.
(9) The working die is used in a coining press to create coins.