Definición

• Shell.  A very thin medallic item. Shells are struck of sheet metal and have design on one side only. The back side of a shell is usually a recessed negative of the obverse design. Shells are always struck with a single blow and only moderately high relief can be created in this manner. The design, however, cannot have any steep-pitched relief at any point or the metal will shear and break at this point. Shells are either intended to be mounted against a flat surface, to be filled in with some substance, or, joined together to form a hollow piece, as a shell medal.
  Creating a shell is a form of embossing. It is like repoussé but instead of
  being hammered from the back it is diestruck, with a die force applied to the back. Shells are always made uniface. Special dies, called embossing dies, are used: a face die – like any other obverse die produces the design – and a force or back die whose only purpose is to drive the thin gauge metal into the face die. The force is a mirror image of the face die, though somewhat smaller; it is positive or male and the face die is female, all of the same image. (How embossing dies are made is explained under embossing dies.)
  Shells are far easier to produce than diestruck solid pieces and can be struck on presses of far less capacity than for coins and medals. They do not require the great pressure as coin and medal presses and small shells can even be struck on drop hammer presses. They were an early alternative to diestruck solid pieces and are produced today in essentially the same manner as 200 years ago.
  Shells were often created by the same artists who created coin and medal models
  – who better to prepare small bas-relief designs?  Some popular or appropriate medallic designs were made into shells, more often, however, shells were created for reasons of low cost, to be worn, a larger size than could not be diestruck solid, or for other reasons.
  As uniface pieces, shells formed small decorative designs that could be applied to most any surface. Today we observe these decorative reliefs with holes for mounting, or some form of solder or adhesive on the back of which they were affixed. So versatile were these small decorative reliefs that they were applied to furniture, bookbindings, albums, wall reliefs, altar ornaments, wooden objects, or even other medallic items. Some were used as emblems, logos or nameplates; often wooden cabinets, appliances or leather objects had such shell decorations.
  Because the back of a shell is always blank and needs to be covered; one inspired
  solution was to attach it to a mirror. These are termed shell mirrors.
  Shell medals.  Two uniface shells can be placed back-to-back in such a manner to
  form the obverse and reverse design in imitation of a solid medal. These are called
  two-piece shell medals, or simply shell medals. They are, for the most part, hollow. As such they are lighter weight than a solid medal and certainly a benefit if the piece is intended to be worn.
  Perhaps the most famous shell medal of all is the Thomas Jefferson Indian Peace
  Medallion of 1801. Struck by the Philadelphia Mint, less than a decade old, they did not have a press heavy enough to strike solid medals of greater than 57mm (the Truxtun Medal of 1801 pushed the size to that maximum).
  When the order arrived for an Indian Peace Medal for Jefferson similar to the large oval (hand engraved) Indian Peace Medals made for President Washington, several changes had to be made: It had to be round rather than oval, and it could not be struck solid.
  Instead, from Robert Scot's 4-inch dies, thin plates were struck. Each die was setup with a back die or force. After striking and trimming, the two plates were attached and held together with a wide metal ring with a loop attached. Because these were somewhat handmade after striking, the exact diameter varies (Julian reports the variance from 100 to 105mm).
  Shell medals with other backing.  Attempts to finish off the reverse of shell medals have been solved in several ways. One ingenious method was to print a thick cardboard with a design or inscription, diecut it to the exact size required and affix this to the back of the obverse shell. The skirt of the obverse shell could then be easily folded over to hold the cardboard in place.
  These shell medals are still very light weight and make excellent badges. Such a shell medal was created by James Murdock of Cincinnati for a Theodore Roosevelt Rough Rider Parade Badge (see illustration).
  Shell medal terminology.  Most shell medals have a ring (its called a band if it has no decoration, or a bezel if it is decorated). Most shell medals have been soldered and held together with such a ring, like the Thomas Jefferson Indian Peace Medallion.
  When bound together the separate shells are called plates. Binding the plates in place has been solved in several ways. They can be brazed if the shells are copper
  or bronze (or silver soldered if the plates are silver).
  Or the hollow area inside shell medals can be filled with a drop-in which secures the two plates in permanent position. The drop-in is usually molten lead or solder; this fills the cavity between the plates and attempts to make a the piece more like a solid piece. It also adds weight to the total piece. (However, we have even observed some shell medals filled with sand.) In England the term applied to the drop-in for shell medals, metal or sand, is irreverently called ballast.
  (Note: shell medals are not struck in lead and then bronze plated as described by some unknowledgeable numismatists. The striking in bronze gives the item its design and surface strength; the lead serves only as filler between the two plates.)
  Often the plates have no border or rim in their design so the ring or band (or bezel), in effect, forms the rim of this fabricated piece. If the obverse and reverse shell plates have an extended rim with raised curved edges where one slips over the other, these edges have names. The outer edge is called the skirt; the inner edge is called the slip. The skirt fits over the slip (like women's clothing).
  History of shell medallic items.  An early English shell medal was made for the Society of Loyal Britons bearing a portrait of George III. Issued in 1776, it was made hollow and the two shells were united by a rim with loop. (Brown 207). Earlier shell medals may exist.
  Many other examples can be given of shell medals in numismatics in addition to the Thomas Jefferson Medal, the Theodore Roosevelt Badge and this English Loyal Briton Medal. In the United States a political medal was issued by Lewis Cass for the 1848 presidential campaign (DeWitt LC 1848-9).
  Condition factors.  Because of their hollowness and somewhat thin metal, shell medals are quite susceptible to damage; it is rare to encounter an old shell medal that has not been damaged by a weight falling on and depressing the shell somewhere. Better shell medals – made of thicker sheet metal – could sometimes withstand such blows, thinner ones, obviously, collapse. The fields are not a uniform surface like a solid medal, but often exhibit uneven areas.
  Like solid medals, thin shell medals are also susceptible to corrosion. However, sustained corrosion will eat through the metal and instead of forming pits (as on a solid medal) it will form holes through the thin metal.
   
  Perpetual calendar medals are classed as shell medals because they are made of two or three separate diestruck shell plates. These are assembled and attached by a central rivet which allows the plates to rotate. Matching a month to a year on separate wheels discloses the day of the week to day of the month. Some have a pierced window on the outer plate for this data to show through from the inner plate.
  Hollowback or stamp and stencil medals.  Some medallic work by stencil manufacturers utilize embossing to produce medallic shells. Their work is mostly of thin gauge brass, and struck on drop hammer presses. They are typically low relief, in a wide variety of shapes, and have no finish for their brass surfaces..
  The reverse of these medals are blank, except, perhaps, a ghosting of the obverse design. The reverse is formed by the force, or jack die. (Infrequently these would contain the maker's mark.)  See HOLLOWBACK
  Shell badges.  All or a portion of a badge could be made of shells. Cheaper
  badges are made of a single shell with a pin soldered to the back. More elaborate badges were two-piece shells with ring and loop hung from a ribbon drape. Shell badges containing a tiny photo image were a development from ferrotypes, popular in presidential campaigns (1860- 1888) but were replaced by the celluloid pin.
  Solid base medals can be customize with the attachment of a shell to form a completed badge. These were often in the center of the item and called badge centers.
  Because of their light weight, shells make excellent badges to be used for a brief time, as a parade or convention badge. A shell badge with a moving part, as some political items were made, is called a mechanical shell.
  Cataloging shells.  A shell medal should always be noted in cataloging, otherwise it would be assumed the piece was solid. Remember: These can most always be identified by their lighter than normal weight, and frequently by their areas of collapsed surface.
  References:                                                                                                                                        
  O18  {1959} DeWitt.
  O37  {1977} Julian.
  O41  {1980} Brown.

  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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