Definition

• Sulphides.  Ornamental glass objects – predominantly paperweights – with relief illustrations molded in the glass, the patterns for these devices were most often
  medals or similar glyptic objects. The technique was called incrustation, and the relief devices were called cameo incrustations. They may appear clear, white, silvery or in full color, and for the most part were portraits taken from the obverses of medals. As such, this was an application of medallic art to other fields of art.
  The process of incrustation was first done in Bohemia about 1750 and first called crystallo-ceramie, the first producers were ceramic makers. Cameo incrustations have
  been applied to a wide variety of glass objects including: paperweights, letter weights (somewhat larger than paperweights), glass plaques, tumblers, goblets, cups, plates; flasks and bottles of many kinds (including scent bottles); vases, obelisks, candlesticks; utilitarian objects as buttons and doorknobs, and finally, even jewelry. The famous French firm of Baccarat made sulphides from mid- nineteenth century to the present; other manufacturers included Clichy and Saint Louis in France and the John Ford Company in Scotland.
  Much of the pleasure of collecting sulfides is to be able to locate and match up the medal from which the relief was taken. Thus the collector is able to identify from the medal the person portrayed and the artist. Only in a few rare instances was any inscription (or identification) molded with the relief incrustation; and unless the artist signed on the truncation of the portrait, his name would not appear on the glass object. (A few sulfides with inscriptions are illustrated in Jokelson, page 93.)
  Because of the method of manufacture the size of the relief incrustation would be exactly that of the medal (except for slight shrinkage after cooling in the mold).
  Thus the device would be the same on the glass object as it would be on the medal.
  Technique of making a sulphide.  A negative plaster mold was taken of a medal whose device was desired for a cameo incrustation. A special clay-glass paste was used to form a positive cast from this mold; the clay cast would then be trimmed to the exact size of the relief part to be reproduced. The clay could be slightly bent. That is how you could have flat medal designs on a round bottle or cup.
  The surface of the clay was then treated for the color or transparency of the incrustation. If it was to be clear, it was coated with a molten glass substance; if silver was wanted, it would be coated with silver dye; if in full color it would have to be painted. Should the clay be left untreated, a small portion of its surface would adhere to the glass object and take the color of the baked clay, somewhat of a chalky color.
  The treated clay was then positioned in the mold for the glass object. The mold was most often of several parts and would be assembled into place. Molten glass was then poured into the mold containing the clay relief. After the object had cooled the mold was disassembled, the object was removed. The clay would then be broken away and discarded. Only the treated surface would adhere to the glass object, it would appear in three dimensions and contain the color or clearness desired.
  References:                                                                                                                                   
  X5 {1968} Jokelson.

  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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