Definizione

• Electroplating.  A very thin coating of metal applied by electrolysis to a base metal item to improve its surface metal, color or finish. Electroplating has tremendous advantage in that it can coat an existing manufactured product with a coating – often a precious metal – at much lower cost than making the item in the more expensive metal. Known as electrodeposition, the process uses electricity (in low voltage direct current), a tank filled with a bath containing a salt of the metal being plated (the solution is called an electrolyte), two electrodes, one of which is the item being plated and the other supplying the source of the metal. The first electrode is called a cathode, it is the item to be plated and is called the work; the other electrode is the anode, it is the source of the metal, as copper, silver or gold.
  Electroplating creates a new surface over a metal base that must be thoroughly
  cleaned and free of corrosion, dirt and grease. The new metal must bond with the base metal. Metals that alloy together are easily bonded, as copper and gold; those that do not
  – gold does not bond to iron, for example, or aluminum – it must first be electroplated with a metal that does. Thus iron must be electroplated with copper or nickel first, then goldplated.
  For coins and medals, few coins are ever electroplated (and never at a mint in modern times – any plating of coins is always done outside a mint). Medals, however, are excellent candidates for changing color and finish and medal makers are required to provide a variety of plating services. Electroplating gold and silver on bronze medals are often done for award medals, creating additional classes of awards by goldplating or silverplating. Even Olympic medals are electroplated to create their gold and silver award medals.
              Electroplating is closely related to electroforming. In electroplating, an
  existing object, completely formed, is coated with a thin layer of desired metal. In electroforming the layering becomes the object. A pattern or matrix (also called mandrel) is used to shape the electrodeposited metal. After it is formed the piece is separated from its pattern). This is how a galvano or dieshell is made (as for reducing and cutting a die), or an object familiar to numismatists, an electrotype of a rare numismatic item.
  Preparation of medals to be electroplated.  Medals intended to be electroplated are struck in the same plant that also contains a finishing department. In the finishing department are the tanks for electroplating; large tanks for copper plating and making galvanos, smaller tanks for silver, even smaller tanks for goldplating.
  The medals must be fully struck up, trimmed and edge lettered. Often they are ideal as they come from the press room if no oil or grease has splattered on any surface. At this stage the surface is called coin finish (struck but unfinished). They are then metal cleaned by degreasing or ultrasonic cleaning to remove all surface debris and any contaminates. Any chemical cleaning will alter the surface creating an activated surface – but this is ideal to be plated.
  Electroplating medals.  After careful cleaning each individual medal is placed on a rack that will be lowered into the electrolyte solution. More than one medal may be on a rack, and numerous racks may be in the tank at the same time. However, the total surface area of all the medals cannot be greater than that of all anode surfaces placed in the tank as a source of the plated metal at the same time.
  The surface of the medals must conduct electricity, perfect if these are copper, silver or alloys high in these metals. An electric circuit must be formed with the medals
  in the circuit. The medals touch the racks, the racks are in contact with a bus bar overhead, and this is connected to a rectifier near the tank. From the rectifier the electric circuit continues by being in contact with another bus bar from which the anodes dangle in the electrolyte solution.
  When the electricity is turned on, the AC current is changed to a very low DC current by the rectifier. This current is carried to the anodes and ions of the anode metal leach or pass into the electrolyte solution. The anode is sacrificial; it wears away like a bar of soap as charged particles of the metal enter the solution, replacing ions
  of metal already in the solution which deposit on the medals. The medals are cathodes which attract the ions of the anodic metal. The deposition continues as long as the circuit is complete and the current is on.
  Many factors regulate the rate of deposition, and many things can go wrong (see electroplating anomalies below). Usually a plating can be observed in twenty minutes or so. A normal coating of a thousandth of an inch might take four hours. An extra heavy coating might require eight hours or more. (In the 19th century some items were marked identifying the thickness of this plating, "XX gold" more than normal, "XXX gold" thickest plating of all.)
  The electroplated metal is a thin coating. It will have the same properties on the surface as solid state of this metal. However, since it is a thin coating it can be worn off easily. Plated medals can be given a patina finish, but care must be taken as any relieving could remove the thin coating. Plated medals are almost always protected with a lacquer coating.
  Marking, bleeding and test cuts.  Plated medals wear at the high points. Often a nose (high point) on a portrait is the first to display the under composition, the base metal. In the rare instances when coins were plated – Henry VIII greatly debased his coins near the end of his reign by silverplating copper coins – the silver wore off to expose the copper base metal. The king was nicknamed "Old Copper Nose" because of this.
  Since silverplated metal can look the same as solid silver, the practice of hallmarking was created as early as 1300 to mark silver objects and guarantee their FINENESS. Plated metal is not required to be marked, solid precious metal objects – gold and silver – are so required. Hallmarking has continued for 700 years into the 20th century when highly industrialized countries passed stringent laws to identify fine gold and silver (1904 in England, 1906 in the United States).
  A solid gold medal of 24 karats (or even 22 karats) will weight twice what a goldplated medal of the same size will weigh (in general), but it will look the same! Copper or bronze medals that are gilded will have a specific gravity of about 8.94, while 24 karat gold is 19.32.
  In order to ascertain the under composition some unthinking persons will make a test cut on the edge. In an attempt to make a visual assay of the base metal they will attempt to cut through the plated layer to observe the under metal. If this can be observed, its color can identify, somewhat, its composition. Copper bleeds pink, silver bleeds gray. (For a list of these colors see bleeding.)
  But the practice of test cutting is observed on solid medals as well as plated medals. A nondestructive test is preferred – as specific gravity – than to damage a coin or medal by cutting into its edge. Such a piece is thereafter a damaged item. A test cut should never be performed by anyone (and only professionals should perform a file cut).
  History of electroplating.  Primitive batteries were the source of the electric current in early electroplating. As soon as the Italian Alessandro Volta developed the voltaic pile in 1800 this could create a feeble current. Michael Faraday, in England, discovered electromagnetic induction in 1830s that improved the generation of the electric current. But it was for the German Moritz Jacobi to develop the process he called "galvanoplasty" that true electroplating was born. Jacobi and another German, Ernst Werner von Siemens, were granted the German patent in 1839. Two British cousins, George Richards Elkington and Henry Elkington, further developed the techniques and patented the process in England in 1840. But it wasn’t until 1847 that silverware manufacturers Rogers Brothers brought this technology to America.
  Batteries were still required as late as the 1880s when Thomas Edison created generating plants that could provide constant electric current. Dynamos generated direct current providing the necessary current until the rectifier was invented in 1940. The rectifier could process any current (including American alternating current) into the required low voltage direct current required for electroplating and electroforming.
  Jewelry field involvement.  Tableware manufacturers were the first to embrace
  electroplating. A utensil struck in copper and silverplated can be made for about one-sixth the cost of sterling or fine silver. But it was the jewelry industry that developed electroplating, even utilizing other metals for aesthetic beauty. Rhodium, iridium, palladium, nickel, have all been electroplated on jewelry items.
  At various times in the last century jewelry firms have manufactured medals and medallic items. These are usually given finishes (highly reflective, polished surfaces) typical of the jewelry industry and many of these are electroplated. These finishes differ from the matte and proof surface from a mint, or the many finishes an experienced medal manufacturer could produce.
  Electroplating anomalies.  Electroplating requires an experienced operator because of the many variables. These include: composition, cleanliness and surface finish of the base metal, composition and purity of the anode, composition of the electrolyte solution, pH, temperature and agitation of the solution, throwing power of the solution, free cyanide, other salts and impurities in the solution, voltage and current density, area of exposed anodic metal.
  To the observer, anomalies of any of these variables might result in an uneven, spotty, discolored or too thin a plated coating. The advantage in medallic work is that an item can be plated again to cover most any unsatisfactory original plating.
  Reverse plating.  The top coating of a metal object can be removed, as easily as
  a coating is deposited. Reverse plating removes the outermost molecules of a metal item. This is done to remove a corrosion that cannot be eradicated any other way (or to recapture gold, say, from an item to be scrapped). Reverse plating is accomplished by switching the electric current; the work becomes the anode, the anode becomes the cathode, the salvaged metal is deposed on the anode.
  References:                                                                                                                               
  F1 {1949} Blum and Hogaboom.
  F2 {1954} Graham.
  F3 {1974} Lowenheim.
  F4 {1986} Rubenstein.
  F5 {1987} Romankiew.

  excerpted with permission from

  An Encyclopedia of Coin and Medal Technology

  For Artists, Makers, Collectors and Curators

  COMPILED AND WRITTEN BY D. WAYNE JOHNSON

  Roger W. Burdette, Editor

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