VOCABULARY TERM: OPEN FACE DIE

Open Face Die. A striking die used without collar or restraining ring. Open face dies are suitable for multiple striking and are shaped like the diestock from which they are cut, their image being engraved into the smoothed flat top of the diestock cut to proper size; the image occupies the central portion of the die's top surface with a wide margin surrounding the design.

Extremely versatile, open face dies can easily be used in most medal presses, and are adequate for all size struck medals one-half inch and larger; they are particularly advantageous for all medals too large to be coined – over 2 ? inches in diameter – up to struck medallions six inches in diameter. They cannot be used for coins.

History. Open face dies came into use during the French development of the art medal in the 1880s. They were the direct result of larger and stronger presses that could accommodate the striking of larger pieces. Open face dies allowed large medals to be struck rather than cast for the first time in substantial production runs.

Thus the acceptance of open face dies spread to countries with active medal plants and their use was universal by the first decade of the 20th century. This important development of a large size striking die – along with the reducing pantograph from oversize modeled relief sculpture for the medal design – were the three major factors leading to the modern art medal.

Open face versus collar dies. All dies are made for a specific striking process. The process determines the kind of press and the press determines the kind of die. Open face dies are in contrast to collar dies (also called coining dies) that are machined to the requirements of the coining press and the use of the collar. There is no margin on a coining die, its striking surface is at the end of a long neck that fits within the opening of the collar.

The circumference of the coining die – nearly the same as the diameter of the struck piece – must be machined within hundredths of an inch smaller than the aperture in the collar. Obverse and reverse dies must enter this aperture – called the coining chamber – strike a blank and retract from this opening.

Open face die characteristics. In contrast, open face dies have no collar, do not have to enter an aperture or opening and have no neck or shoulder; they are not machined to a silhouette to accomplish what coining dies have to accomplish. Open face dies have a flat surface at the top of the die – the design is sunken into this flat top surface within a wide margin.

Open face dies take the shape of the diestock from which they are made, and since most diestock is circular most dies are circular (but diestock and dies can be square, rectangular or even hexagonal). Large open face dies look like small round hat boxes and are, indeed, called box dies in England.

Open face dies are usually twice the diameter of the struck pieces from that die (see chart, Typical Die Diameters). The greater diameter provides greater mass to the die to enable it to strike very large medals (up to six- inch diameter), very heavy thickness in relief or gauge –all under very high pressure. Without such additional mass the dies would not have the strength to do this nor sustain long production runs.

Despite the fact open face dies cannot be used in coining presses, they may, however, be used on a variety of striking presses. This includes hydraulic, knuckle-joint and some punch presses.

Also all coined pieces are usually mechanically fed (obviously all high-speed coining is mechanically fed); all pieces struck from open face dies must be hand fed. Coining is high speed; striking with open face dies is much slower, where a manual operator feeds and ejects struck pieces in synchronization with the cycle of the press.

As a final point of comparison between open face and collar dies, coining requires a pre formed (upset) blank. A blank for open face dies need only be the proper gauge but can be the same size – or somewhat larger – than the intended struck piece. All pieces struck from open face dies must be trimmed.

How open face dies are made. The diemaker must know the process for which a pair of dies are intended, he receives a work order which states the type of press and a diameter to cut the dies. He is also furnished a metal or epoxy pattern (dieshell) from which to cut the die. He will mount the pattern dieshell in the die-engraving pantograph and mount a proper diameter diestock. For an open face die he must choose a diestock wider than the intended diameter of the medal is chosen.

The pantograph is set to tracing the relief of the pattern, and by means of a long bar this is transferred to the cutting point which mills (cuts) the rises and falls of the relief into to center of the steel diestock. This continues for the full diameter of the pattern, reducing the design in the prescribed ratio to cut the exact diameter required in the diestock. Usually three separate cuts are made to ensure all cavities of the relief pattern are cut into the die. See pantograph.

Open face dies, while they could be handcut, are almost always cut by pantographic reduction. Thus highly detailed designs can be mechanically cut with an assurance of close fidelity to the original design. After the final cut, the die is examined, proved by taking a lead impression, and if satisfactory, the die is hardened by tempering.

Nothing more is done to the die. It is not trimmed to a silhouette to fit a collar as a coining die. It is ready for striking after it has been hardened and normalized. See heat treating.

Orientating open face dies. Once the dies have been inspected, approved, hardened and before they go on a press they can be marked in some way so they line up, so the die alignment of pieces stuck from those dies will have a perfect orientation of their obverse and reverse axis. This can be done in several ways.

For dies that are cut from bar stock they will be round in circumference. Orientating a die is to twist it slightly. They can be scribed or marked or painted on the side to indicate that the 12 o'clock position of one will match the 12 o'clock position on the other. The mark, obviously, must be in a position it can be viewed when it is set in a press.

If the orientation is super critical a mechanical device can be created with the pair of open face dies. In the margin on the face of one die – outside the image area of course – can be located a bushing, a hole drilled right into the top margin surface of the die. Into this bushing will be inserted the guide pin. Another hole is drilled into the opposite die in exactly the corresponding position.

This technique, called guide pin and bushing, can be used while the press operates, or if necessary, the guide pin may be removed. Only on open face dies can a guide pin and two bushings be used because of the margin on the face of both dies.

Resulting edges on pieces struck from open face dies. Because there is nothing to restrain the flow of metal when blanks are struck between open face dies, metal extrudes from the edge between the dies. This flange – called flash – grows larger during multiple striking. After the metal is fully struck up this flash is trimmed off. Large round medals can be easily turned on a lathe (with the use of a form mold). Irregularly shaped medals must be trimmed by hand or require a trimming tool (with trimming punch and plate).

For those medals trimmed on a lathe, tool marks, called annular rings, are often seen on the edge running parallel with the sides of the medal. Thus this type of trimming and these marks are diagnostic evidence these pieces were struck with open face dies.

Collars for large medals were used in the 19th century were virtually eliminated by the first decade of the 20th century. Open face dies are now universally used for striking all large medals.

Storage of open face dies. Open face dies have an inherent characteristic – they almost never wear out (their die life is greater than most intended use). Thus dies are excellent for such medal programs that require medals over long periods of time.

Such dies are placed in a DIE VAULT for storage. They must be treated to prevent rusting and stored in a dehumidified atmosphere. The face of the die must be protected from rusting, if possible it must be kept without exposure to air. This is done by storing with a struck specimen between the dies – one on top of the other – or by placing Cosmolene, petroleum jelly or a plastic cap over the face, and storing these side by side. The intent here is to prevent moisture from reaching the face of any die.

To read the complete entry on the Newman Numismatic Portal, see:
Open Face Die (https://nnp.wustl.edu/library/dictionarydetail/516424)

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