Electrotype - NumisWiki, The Collaborative Numismatics Project

Electrotype (Galvanocopy)

In the late eighteenth to mid twentieth centuries electrotypes were made as originally officially sanctioned copies of specimens in public collections, including the Ashmolean and the British Museum. They were not meant to deceive, but were to be employed as teaching aids for numismatists who might not be able to see the genuine coins in the collection, and serve as display examples for individuals who wished to be able to have an example of specific coins. The majority of electrotype copies were produced by the British Museum, most under the auspices of Robert Cooper Ready and his sons between 1859 and 1931. A skilled seal maker and modeler, these electrotypes are known by the letters RR stamped on the coin 's edge. They are highly sought-after collectables in their own right. At one point, a large portion of the coin collection was electrotyped, which proved to be widely popular with Museum customers and art enthusiasts. However, later unscrupulous individuals used these electrotypes to deceive the unwary, and the British Museum halted the process.

The coin above shows the superb duplication possible with electrotyping. It is a modern electrotype fake AR double nomos of Lucania, Thourioi, 25mm, 17.08g. Obv: helmeted head of Athena, right, helmet decorated with Skylla scanning distance, griffin on neck guard. Rev: bull butting right; in exergue, fish right. It is a copy of original in British Museum made by Robert Ready with the edge stamped RR.

While the obverse and reverse are near perfect copies, the weight of an electrotype is usually wrong, and the edge of an electrotype is usually obvious. See the fake coin edge study images in the Fake Coin Reports for examples of electrotype coin replica edges:

https://www.forumancientcoins.com/fakes/thumbnails.php?album=39

Wikipedia

Electrotyping (galvanoplasty) is a chemical method for forming metal parts that exactly reproduce a model. The method was invented by Moritz von Jacobi in Russia in 1838, and was immediately adopted for applications in printing and several other fields.As described in an 1890 treatise, electrotyping produces "an exact facsimile of any object having an irregular surface, whether it be an engraved steel- or copper-plate, a wood-cut, or a form of set-up type, to be used for printing; or a medal, medallion, statue, bust, or even a natural object, for art purposes. In art, several important "bronze" sculptures created in the 19th century are actually electrotyped copper, and not bronze at all; sculptures were executed using electrotyping at least into the 1930s. In printing, electrotyping had become a standard method for producing plates for letterpress printing by the late 1800s. It complemented the older technology of stereotyping, which involved metal casting. By 1901, stereotypers and electrotypers in several countries had formed labor unions around these crafts. The unions persisted into the 1970s, but by the late 20th century, after more than a century in widespread use for preparing plates, the two technologies had been bypassed by the transitions to offset printing and to new techniques for the preparation of printing plates.

Electrotyping has been used for the production of metal sculptures, where it is an alternative to the casting of molten metal. These sculptures are sometimes called "galvanoplastic bronzes", although the actual metal is usually copper. It was possible to apply essentially any patina to these sculptures; gilding was also readily accomplished in the same facilities as electrotyping by using electroplating. Electrotyping has been used to reproduce valuable objects such as ancient coins, and in some cases electrotype copies have proven more durable than fragile originals.

-- https://en.wikipedia.org/wiki/Electrotyping

You Tube:

Metropolitan Museum Video on electrotyping: https://m.youtube.com/watch?v=iTytvWs5nV8

References

Head, B. A Guide to the Select Greek and Roman Coins Exhibited in Electrotype 1880. Department Of Coins And Medals, British Museum. (London, 1880).
Wayne, S. Classical Deception: Counterfeits, Forgeries and Reproductions of Ancient Coins. (Iola WI, 2001).