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Book VI gems: diamond, emeralds, sapphire, topaz, chrysoberyl, carbuncle, jaspis

Book VI gems: diamond, emeralds, sapphire, topaz, chrysoberyl, carbuncle, jaspis Page of 251 Book VI gems: diamond, emeralds, sapphire, topaz, chrysoberyl, carbuncle, jaspis Text size:minus plus Restore normal size   Mail page  Print this page
116
DE NATURA FOSSILIUM
a weaker brilliancy than the true and are scratched by a file. Less cleverly they attempt to produce a false carbunculus by cementing two pieces of glass together, or better two pieces of quartz, with a thin layer of minium between them. Minium is called "dragon's blood" in their workshops. Since both quartz and glass are scratched by a file this deception is not difficult to detect even when the stone is in a ring or closed setting. When it is taken out of its setting the cementing can be seen and one part separated from the other. These gems are made in a number of different ways and are called doublets. By using two pieces of glass or quartz with different dyes between them rogues produce all manner of colored trans­parent gems. The finest carbunculus, which we call rubinus (spinel), is made from a piece of Carthaginian garnet and quartz cemented to­gether with the garnet on top, the quartz on the bottom and a dye be­tween them. Since the garnet is not scratched by a file this fraud cannot be detected unless the gem is taken from its setting. In a similar fashion, according to Pliny, sardonyx is made form ceraunia which is cemented to gems, sometimes white, sometimes black, sometimes red. True but worth­less gems are sometimes made into valuable gems in this way, for example, amethystizon from amethyst; diamond from quartz, colorless corundum, or beryllus similar to quartz. Certain amethysts are perforated and filled with minium or are deeply engraved and thin sheets of foil cemented beneath them so that they may be passed as carbunculi. Quartz, corundum and beryllus are given the hexagonal form of diamond and true diamond is cemented on top of them since it is a common practice to make diamond doublets. These artificial diamonds and carbunculi are very similar to true gems when set in a ring but when they are taken from the setting and the foils or dyes removed the fraud is apparent. Quartz is scratched with a file even when set in a ring and can be readily identified in this way. Moreover, with transparent gems, the portion that receives the light appears to be brilliant clear, the portion that reflects the light, if it only reflects it, appears to be even clearer. With all other gems, of whatever color they may be, they reflect the same color. The varicolored gems are even more brilliant. This property is best observed in gems that are angu­lar or rounded like a shield.
Gems have one, two or more colors as was mentioned in Book One and I shall review them here in a few words. Many gems have only one color, for example, quartz, asterios and diamond are colorless; smaragdus, beryl­lus and prase, green; sapphire, blue; carbunculus and sard, red; sandastros and chrysolithos, yellow. When a gem has two colors these may be distinct or mixed. Several have the colors mixed, aphrodisiace being reddish white, xanthos, yellowish white and the three species of batrachiles, reddish black. Examples of stones with two distinct colors are, apsyctos with reddish veins in a black stone, nasamonites with black veins in a red stone, helio­trope, with blood-red veins in a leek-green stone. The opal has three intermingled colors, flame, purple and green. According to Jacchus the
Book VI gems: diamond, emeralds, sapphire, topaz, chrysoberyl, carbuncle, jaspis Page of 251 Book VI gems: diamond, emeralds, sapphire, topaz, chrysoberyl, carbuncle, jaspis
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