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Electrotype.  A medallic or numismatic item made by electrolysis; a galvano or electroform. An electrotype requires a mold or pattern, which must be negative to produce a positive item. It creates a shell of one side of a coin, medal or plaquette; two shells are required to make a two- sided item. To give the item a solid feel it can be filled with metal, usually lead, called a drop-in. By bringing two sides together it creates a seam around the edge, which is diagnostic of most electrotypes. The metal required of electrolysis must conduct an electric current, thus metals normally used for coins – copper, silver, gold – are also excellent to use in electroforming. While such pieces were formerly called electro in the numismatic field, the full term is used today.

Status of electrotypes.  There are two areas of electrotype manufacture, one of which may be considered of questionable status. No one would dispute the making of electrotypes from new models and patterns as works of original art. The questionable area is replicating existing coins and medals. By using a coin or medal as a pattern, a mold may be taken of it, and this mold used as the pattern for an electrotype. Collectors consider this a "counterfeit" and would shun it.

Technically, however, an electrotype made from a coin or medal is a custom copy. Several museums have offered this as a service for replicating specimens in their collections. (The British Museum did this for a nearly forty years, see history below.) Thus knowledgeable numismatists recognize electrotypes as either original works of art or replicas for legitimate research or study.

How electrolysis is used to make an electrotype.  The mold or pattern for an electrotype must be negative to make a positive electrotype. (Thus a mold is made from the coin or medal to be replicated.) The mold may be any materialmetal, plaster, epoxy or other material. It is then coated with bronze powders or graphite to make it electrically conductive; the powders also act as a release agent when the mold and electroformed cast are separated.

The coated pattern is wired, to carry the current to an overhead bar (called a bus

bar). The wired pattern is suspended in an electrolyte solution in a tank. The mold is the cathode, and the source of the metal to from the item is the anode. The current is furnished from a rectifier (which converts alternating current to direct current and supplies the electric current in very low voltage).

The current is turned on and electrodeposition begins. Molecules of metal (actually ions) from the anode pass instantly into the electrolyte solution; existing ions of medal already in the electrolyte then deposit on the cathode. A thin shell is formed and the longer the pattern is left in the tank with the current on, the thicker the shell becomes.

The pattern – with the newly made electroformed shell still attached – is

removed from the tank and the two are separated (easily pried apart if there are no undercuts). Two shells are electrically cast separate to make a two-sided piece. This is usually in the same tank at the same time so the two pieces will have the same composition.

The shells are roughly trimmed to size, and the shell with the greatest cavity (usually the obverse) is laid flat. A drop-in of molten lead is poured into the shell and while still molten the opposite shell is placed over it in position (the axis of the obverse must match the axis of the reverse). After the lead solidifies, and the piece can be handled, the edge is burnished to even out it's surface.

If it is a copper electrotype, it is bright red all during this stage. It must be given a patina to protect and color its surface. A silver electrotype is generally highlighted. Gold electrotypes are customarily left intact (since the gold finish is stable).

History of electrotypes.  The first electrotypes were made with primitive batteries in both Europe and America in 1840. Within a decade small glyptic objects including coins and medals were being replicated. By 1859 in New York City Samuel H. Black had advanced his techniques to produce plaques up to two feet square and had created his Declaration of Independence Plaque with five American medals replicated on it. (See illustration.)

In England the British Museum was electrolytically casting copies of coins in their collections for sale to the public. Robert Cooper Ready, an antiquarian, was given permission to replicate by electrotyping any coin, medal, seal or gem in the museum's collections. When he died his estate contained over 22,000 such electrotypes.

Ready's sons, August and Charles, carried on this practice well into the 1880s but

by this time to differentiate their casts, they placed the initials R, RR or MB on the edges of their electrotypes. Today many of these Ready electrotypes are rarer than the originals and are in demand by numismatists (but shunned by collectors who see them only as "counterfeits"). See Forrer (5:53-54).

Detecting electrotype copies.  Often the seam where the two sides are joined is the most obvious evidence to identify an electrotype. Other diagnostic evidence is the difference in weight between the original and the electrotype (the original being heavier). Also the specific gravity will differ. An original is one homogeneous mass, the electrotype is made of copper with a metal filler, usually lead or solder. The surface will be a pure metal – pure copper, pure silver, or in rare instances, pure gold – since an electrotype is usually made with pure anodes (but can be placed in different tanks, or different anodes can be introduced in the tank, for different metal deposits).

Also an electrotype piece will not pass the ring test, with a duller resonance

than a struck piece; it will have a lower tone or even a dead thud. However, the edge is the most viable place to notice the difference between a struck piece and an electrotype – the seam should be evident. Some dishonest electrotypers even tried to evade that by machining the two shells so that one had a complete, smooth solid edge, the other have no edge at all, and the seam was at or near the rim/edge juncture.


E3    {1902-30} Forrer 5:53-4 (on Robert Ready, electrotyper).

NC6 {1960} Peck, p 90, note 1.

N19  {1998} Bowers, p 110.

excerpted with permission from

An Encyclopedia of Coin and Medal Technology

For Artists, Makers, Collectors and Curators


Roger W. Burdette, Editor

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