Definizione

• Electroform, Electroforming.  A metal object made by electrodeposition, a galvano or electrotype, and the process of its creation. Electroforming, like electroplating, is a form of the electrolysis of metal. The two processes differ in that electroplating coats an existing object with metal, electroforming creates a complete, newly formed object. Electroforming requires a matrix or pattern, upon which metal is deposited, building up in time the required thickness of the object.
  Electroforming is ideal for reproducing bas-relief forms because of the ease
  of depositing metal on their three-dimensional surfaces, and the extreme fidelity in reproducing detail – including minute detail often found on coins and medals. Electroformed galvanos are ideal patterns to be used on die-engraving pantographs.
  The important criteria for this galvano casting, called a dieshell (when it is used on the pantograph to cut a die), is that there can be no undercuts in any pattern and that all relief have a very slight bevel. In the field of coin and medal die striking this requirement of no undercuts and slight bevel in the pattern is an extreme benefit because dies cut from electroformed galvanos thus will be assured of having no undercuts and a slight bevel in every die made from these. If the electroformed dieshell can be removed from its matrix, then it is guaranteed the die (made from that dieshell) will be able to strike and withdraw from its struck piece!
  Electroforms may be either positive or negative. They produce the opposite of their matrix. A positive pattern would create a negative electroform or dieshell; the pattern used in a die-engraving pantograph to cut a die must be negative. Or the matrix may be negative to electroform a positive galvano, as a hubshell (to cut a hub on the pantograph). Or from the negative matrix may come a positive electroform as the end product itself, a plaque, or electroformed shell.
  Requirement of a bevel.  The important criteria for any galvano casting is that there can be no undercuts in any pattern and that all relief and lettering have a very slight bevel. In the field of coin and medal die striking this requirement of no undercuts and slight bevel in the pattern is an extreme benefit because dies cut from electroformed galvanos thus will be assured of having no undercuts and a slight bevel in every die made from these.
  The amount of the bevel (also called draft or taper) on the sides of all
  design and lettering is critical. On galvanos a 10° bevel is satisfactory. Newly formed electroforms will easily release from their matrix with this bevel. For technical reasons
  a bevel on dieshells and hubshells must be 15° or more. (A bevel of 5° or less is called “hanging taper” and this is impossible for a galvano to release from its pattern, or a die to release from the struck piece.) If the electroformed dieshell can be removed from its matrix, then it is guaranteed the die (made from that dieshell) will be able to strike and withdraw from its struck piece!
  How electroforms are made.  Electroforms are made in an electrolytic tank containing an electrolyte solution. First the pattern is coated to conduct an electric
  current and wired to a circuit. The pattern becomes the cathode in the solution of the electrolyte. An anode of the metal in which the object is to be made is also wired to the circuit and connected to a rectifier that supplies a very low voltage electric current (which must be DC, direct current).
  In seconds after the electricity is turned on the metal of the anode in the form of ions leaches from it, passing into the solution. Ions of the same metal already in the solution deposits on the cathode (the pattern). This is a continuous process as long as the electricity is on. It is allowed to continue for 24 hours a day until the required thickness is deposited. About three days is required for a 1/8-inch thickness.
  Electroforms can only be made in a metal or composition that is electrically conductive. Copper, silver, nickel, gold rank high in this characteristic – the metals so widely employed for medallic work – but other metals can also be electroformed: platinum, palladium, iridium, chromium, others. Iron can be electroformed but is brittle, chromium is unsuitable because it cracks in thick deposits.
  (Two metals can be electroformed on one object, but this requires separate anodes for each metal, with ions of that metal in the electrolyte solution. It is better if these
  are in separate tanks and the pattern moved from one to the other. In the numismatic field a copper electroform may be coated with an outer layer of nickel – for color or hardness. [This was done for James Earle Fraser when he had electrotrials of his Buffalo nickel designs made by Henri Weil prior to submitting his models to the U.S. Mint.] In the jewelry field silver electroforms are coated with iridium, for hardness, the color of silver and iridium is about the same, indistinguishable in the final form.)
  Preparing the pattern.  The pattern for the electroform may be any material that can withstand being submerged in a tank of electrolyte solution for several days and hard enough to sustain the buildup of metal on its surface. This material can be metal, plaster, wood, plastic, epoxy, stone – any hard surface. (Obviously clay cannot be used, but it is easy to make a plaster cast of a clay model for use as the pattern for electroforming.)
  If the pattern is porous (like wood) it must be given a sealer, as with shellac. In fact, careful modelers will seal every model (even plaster) to provide a hard, continuous, nonporous, surface.
  The model for the electroformed pattern – also called mandrel, core pattern, or former (in England) in addition to matrix –contains the design in relief. It is for this reason it is prepared by a sculptor who must know three things: (1) be knowledgeable in bas-relief sculpture, (2) know the needs of the client and mint or medal manufacturer, plus (3) the requirements of the die making process: proper bevel of all relief, no undercuts, type of press to be struck on, height of relief requirement, die camber necessary, intended proof surface areas if any, required flange around the model and such.
  Ideally the model should have a minimum of 1-inch flange surrounding circumference on all sides. When a model is prepared for forming a dieshell or hubshell a similar flange is required to be reproduced on the electroform. This is necessary to hold the dieshell or hubshell in place (by clamps or bolts) on the die-engraving pantograph.
  The pattern, made from the sculptor's model, provides the surface that is exactly what will be reproduced in electroformed metal. This surface must be the same size, the correct configuration, the exact camber as needed. Its design must be exactly what will be reproduced. Electroforming is extremely high in its fidelity of reproducing exactly what is in the pattern. (Medal makers motto about design: "if its in the model, it will be in the medal!")
  Making the pattern electrically conductive.  The approved pattern, free from any pores, minute holes, cracks, or undercuts is cleaned, dried and sprayed with compressed air. It is then coated with bronze powders, to make a metallized surface. This is done for two reasons: it makes the surface electrolytic conductive (the electric current passes along this coating); and also as a release agent or parting agent after the electroform is completed and it is time to pry the pattern and cast apart.
  The coated pattern then must be wired. A copper wire is attached to the pattern in such a way it comes in contact with the metallized surface. Also the wire must be sturdy enough to support the weight of the pattern, plus the weight of the electroform, as its being formed.
  The reverse of the pattern is then stopped-off. All surface that is not wanted to be coated with copper, all nonconductive surface – obviously the back and the edge of the pattern – must be coated with a stop-off. A coating of wax, beeswax, paraffin, rosin, or a combination of any of these. (The temperature of the electrolyte in the tank must be kept below the melting point of this stop-off, however.)
  Immersion in the tank. The wired and stopped-off ensemble is then placed in the tank containing the electrolyte solution. The wires are placed in contact with a bus bar above the tank which supports the pattern while it remains in the solution. (No toning or corrosion can be at the contact point where the wire touches the bus bar – the electric circuit must be free to flow at this crucial point.)
  The electrolyte solution or bath is composed of chemicals which make it electrically conductive. Depending upon the metal being sourced from the anodes, the bath is composed of cyanide acid, fluoborate, sulfamate, or chloride sulfate. The metal to be deposited (in the form of ions) must be placed in the solution as metal salts before any electroforming can take place. Copper, silver and gold respond best in a cyanide bath.
  Completed circuit.  The circuit is then complete. Electric current is sent into the rectifier. In turn it sends out very low voltage direct current. This travels from the rectifier to bus bars along the sides of the tank upon which are hung the medal anodes (again with clean contact points). Then through the electrolyte solution, to the surface of the cathode, up the wire to the overhead bus bar returning to the rectifier.
  The current gives an electrical charge to the anode and the cathode. Ions of the
  anode are positive and they are drawn into the electrolyte. The positive ions in the solution are attracted to the cathode which is negatively charged. This exchange continues as long as the current is on. In as little as 15 to 20 minutes enough metal is deposited in a thin coating on the pattern to be seen by the naked eye.
  The process can be speeded up by various methods, primarily increased temperature or agitation of the bath, or both. Even so it requires from 40 to 70 hours for a 1/8-inch thickness, typical of a coin or medal electroform.
  Removing the electroform.  When the required thickness has formed (this can also be termed cast and the product is an electroformed casting), the ensemble is removed from the tank. The electroform is pried off the pattern, the bronze powder aids in this release. A dull knife blade is inserted and twisted between the pattern and the electroformed casting at several places. (If it still sticks, a trick of the trade, is to blow compressed air between the two.)
  If the pattern is metal and if there is any suspicion that it would be used again in the future the wires are left intact for storage. If the pattern is plaster, it may not be used again; it is discarded. For production run electroforms, the matrix must be nondestructive metal patterns that can be used over and over again.
  At this point the electroform is inspected, any touchup may be done (usually unnecessary since the fidelity of the electroformed casting is so close to the pattern). The
  touchup – by chasing – usually removes stray nodules of metal; these are formed by any dirt or trapped gas that had been on the surface of the pattern.
  Backing up the electroform.  Since electroforms are relatively thin they can be strengthened by adding supplement metal to the back. Lead or solder is used for this purpose and it is called drop-in. The thinnest spots – usually the high points on the obverse – are areas often strengthened with a drop-in.
  If two electroform shells are to be attached – as to make an electrotype coin or a galvano medal – the entire reverse of one is flooded with lead before the second is attached (by floating on this liquid lead surface) to make a "solid" medal when the drop-in lead cools. It requires great skill to create such a double-sided galvano without an obvious seam around the edge.
  Since the drop-in metal is cheaper than copper, silver or gold, electrotypers who wish to cut corners make a thinner casting of the pure metal, and use more lead as the drop-in. Other metals could be used as a drop-in, but lead is the most useful (because of its low cost and low melting point). If left uncolored the drop-in is observed as the silver-gray color of lead; it may, however, be disguised as a dark metal by coating or coloring. (A test cut will identify the lead however.)
  Storing electroforms.  Since electroforms are permanent metal patterns, they are most often chosen for storage. (The clay or plaster models could be stored, but they are too impermanent.) In storage the metal pattern cannot be stored leaning against something either horizontal or vertical (in time this could cause defirnatuib). Instead the connecting wires are left on the pattern and is stored on suspension racks hanging undisturbed by these same wires.
  Final electroform.  The electroform is a dieshell if it is negative and intended to be mounted on a die-engraving pantograph to cut a die. (The pattern must have been positive to cut a negative dieshell.) If the pattern was negative the electroform would be positive for a hubshell (for cutting a hub on the pantograph). Also a negative pattern would produce a positive shell or plaque if this is what was required.
  Dieshells and hubshells are left with their flanges intact in their as-cast state with no finishing required. A positive cast, as for a plaque, would be trimmed then sent to the finishing department for any finish required. (Further treatment of an electroformed shell would depend upon how it would be used.)
  Electroforms as the end product, the final object as an art object itself, are thin and one sided – ideal candidates to be mounted or framed. We have observed hundreds of electroforms in frames (like a three-dimensional bas-relief picture). Portraits, beaux-art, sentimental scenes, have all been made by electroforming and framed. The Confederate Seal was electroformed in 1873, for example, and was mounted in several ways for sale to the public.
  Advantages of electroforming.  Despite its slow process and its somewhat high cost, electroforms are used in the numismatic and medallic field because they reproduce forms in the same composition as coins and medals – copper, silver, nickel, gold – the so-called "medallic media."
  But even more so, electroforming is used for its extreme fidelity to the pattern
  and its ability to form minute detail. Close to 100% of the detail in the model will be reproduced in the electroform, with detail as fine as half a millionth of an inch! (Theoretically any detail could be satisfactorily reproduced as thin as a few microns!) These advantages outweigh the disadvantages that a scratch on the model will appear on the electroform, and that a small crevice deeper than its width cannot be easily formed.
  Also electroforms are ideal permanent records of bas- relief designs. Should a die break in production, a new one can always be cut from a stored dieshell (an inexpensive insurance). A feature that epoxy dieshells do not provide.
  As a technical factor, copper dieshells provide a better surface for the tracing point on the die-engraving pantograph to ride upon. The contact between the steel tracing point is a smoother contact on copper than upon the carbon surface of an epoxy dieshell surface.
  Electroforming anomalies.  Because there are so many variables in electroforming, a number of things can go wrong. Blisters, peeling, or nodules – the most common anomalies – are a result of dirt on the pattern. Uneven deposition is a result of where the anodes are placed in the tank, they must be near the work to furnish a continual source of metal. Brittleness and thin spots are due to insufficient time in the tank. Spongy deposition is due to chemical failure.
  Electroform diagnostics.  An electroform is usually pure metal: copper, silver, nickel or gold. It is usually a thin shell, less than 1/8-inch thick (but can be any thickness). If its reverse can be observed (as a plaque or single-sided item) the back surface will be rough or smooth, but the most diagnostic of all electroforming will be little round nodules of metal widely spaced on this surface. Also it will have depressed areas on the reverse congruent with high relief areas on the obverse (while not a perfect mirror image of the obverse relief, it will follow the obverse contour).
  Other diagnostics: it may have a gray metal drop-in on any part of this reverse
  surface (particularly at any thin spots or at the point of high relief on the obverse). Electroforms do not ring well.  When two electroform shells are affixed together there will always be a seam on the edge. Electroforms are usually closed off, mounted together, or provide some means for hanging as hangers or bolts soldered to the back.
  In cataloging, electroforms must always be identified as what they are. They may
  be called electroforms, galvanos, electrotypes, electrogalvanic casts (or should the patterns be cataloged they should be noted as dieshells or hubshells). Also they should be noted as positive or negative. It is best not to call them shells, since shells can be cast, diestruck or formed by repoussé as well as by electrodeposition. The size of electroforms should be noted in centimeters and measured from one side of the image to the other side of the image (not from edge to edge since most all will have some flange intact).
  References:                                                                                                                             
  F1 {1949} Blum and Hogaboom
  F2 {1954} Graham
  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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