Gems, imitation

K. Nassau, J. Nassau The Grovrth of Synthetic and Imitation Gems KSchonherr The Growth of Large Crystals from the Vapor Phase... 

The allusions to Democritus by Vitruvius, writing a century or more before Pliny, seem to apply to the real Democritus. Vitruvius says he wrote several works on the nature of things. Seneca attributes to him the invention of the reverbatory furnace, and the art of imitating natural gems, particularly the emerald, though it is probable that here also the real Democritus is confused with the pseudo-Democritus. 

For imitating gems and semiprecious stones, Pliny says that glass was extensively used, and that it was with great difficulty that the imitations could be distinguished from the genuine. Obsidian, topaz, beryl, carbuncle, sapphire, jasper, opal, onyx, and emerald were thus imitated. 

Antonio Neri, who wrote a treatise on glassmaking, first printed in Italian in 1612, refers to This method of imitating gems which I received (or obtained) from Isaac Hollandus when I was in Flanders. Neri s sojourn in Flanders was about 1609. This statement does not in itself necessitate the interpretation of personal contact between Neri and Isaac Hollandus, although von Lippmann calls attention to the fact that Neri, in his work, has not the habit of citing written works as authorities, and that the published works of Hollandus contain no such matter as Neri here describes. 

There are three types of gemstone materials as defined by the U.S. Federal Trade Commission (1) (/) natural gemstones are found in nature and at most are enhanced (see Gemstones, gemstone treatment) (2) imitation or simulated, fake, faux, etc, material resembles the natural material in appearance only and is frequendy only colored glass or even plastic and (3) synthetic material is the exact duplicate of the natural material, having the same chemical composition, optical properties, etc, as the natural, but made in the laboratory (2,3). Moreover, the word gem cannot be used for synthetic gemstone material. The synthetic equivalent of a natural material may, however, be used as an imitation of another, eg, synthetic cubic zirconia is widely used as a diamond imitation. 

The materials most commonly used as gems and ornamental stones are listed in Table 2.9. This is by no means a complete listing of all materials ever used in jewelry or for decorative purposes. There are many worked specimens that are one-of-a-kind, made from unexpected materials that were opportunistically obtained. These often pose problems of identification and consequently of conservation, since once a stone has been worked it loses its natural luster and form. Stones have been altered with dyes and heat for thousands of years, so it does not hold true that just because something is in an old artifact or Grandma s necklace that it cannot be dyed or otherwise not natural. Synthetics are relatively new, but imitations are as old as the stones themselves. If someone wanted a red gem, and there were no rubies available, then a garnet or spinel could be used instead. No emeralds Use an olivine (peridot) or green sapphire. A synthetic must have the same composition and internal structure as the natural material, but an imitation just has to look like the natural stone. 

Spinel is another simple oxide mineral. It is commonly seen today as a synthetic and may be any color. Natural red spinel was most prized as a gem, and usually was used as an imitation of ruby. Some notable pieces in the British and Russian crown jewels include large uncut spinels. These crystals are a deep red color and are distinctive because of their rough octahedral shape. 

Colorless zircon has been used as an imitation of diamond, since it has a very high refractive index. Zircon gems are doubly refractive, which can give them a cloudy appearance. Looking through the top of a faceted zircon, the back facet edges will appear double. Zircons come in many colors, and this gem is often heat-treated to change or enhance the color. 

Jade is the common name for gem-quality specimens of two distinctly different mineral species, jadeite and the massive variety of actinolite, called nephrite. The word jade is derived from the Spanish piedra deyjada, meaning stone of the flank. This refers to its popular use as a cure for diseases of the kidneys and liver. Other minerals that have been mistaken for jade, or used as jade imitations include green jasper (quartz), vesuvian (idocrase), massive grossular garnet, chloromelanite (a mixture of dark pyroxenes) (Table 2.10). 

Plastics appear as a simulant for every organic gem material. They have also been used for imitating pearls, but, unless coated in the ways mentioned above, both early and modem plastics are totally unconvincing. 

Casein was a major plastic in the imitation of organic gem materials. It was developed in the late nineteenth century, and was also known by various trade names such as Erinoid and Galalith . It derived from proteins in the curds of skimmed milk, which were moulded and cured with formaldehyde. 

There are a few modern plasticB that should possibly be mentioned, as plastics are still being used to imitate organic gem materials. It is increasingly difficult, however, to tell exactly vdiich synthetic polymer has been used, and today it is of less importance to... 

Gamosep alous.—Having the sepals more or less imited at their margins. Gem ma.—An asexual bud-like structure found in the capules of Liverworts. Gemma tion.—The process of budding as seen in the yeasts. 

Routes to 2//-[l]benzopyrans have been reviewed <75AHC(18)159, 77HC(31)11, 84CHEC-I(3)757, 96CHEC-II(5)351> and in many cases these methods are readily adaptable to naphthopyran synthesis. However, the specific interest here lies with naphthopyrans containing a gem diaryl imit, a substitution pattern that imposes restrictions on the synthetic approach. 

Balitsky, V.S. and Lisitsina, E.E. (1981) Synthetic analogs and imitation of natural gems, Nedra, Moscow. 

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