GEMS.

New Zealand Graphic, Volume VIII, Issue 33, 15 August 1891, Page 271

GEMS.

EM,’ in common speech, means a precious stone, especially when engraved for an ornament or other purpose. This, putting aside its primary meaning of a ‘ bud,’ is pretty nearly its significance in classical Latin, though in both languages it might be looselyextehded to comprise a pearl. It includes, for instance, Egyptian scarabs, which are often made out of clay or steatite (a variety of talc), Hittite ‘ gems,' for

which limestone and marble, among other materials, were used, Phti-nician scarabs, and the metal signets found in the Mycenae tombs. These are curious and interesting, and some exhibit delicate workmanship, and, occasionally, great artistic skill. The most attractive part of the subject, however, is that which is concerned with the gem proper, and that as it was handled by Greek or Roman artists. Precious stones have always been the most fascinat-

ing of human possessions. Their intrinsic beauty goes for something ; their durability for more. The imagination is tired when we know that the article one touches is exactly the same as it presented itself to human eyes and hands thousands of years ago. The minerals of which the vast majority of the finest antique engraved jems are made were by no means raie or costly. The diamond, for instance, though it occurs in ancient art, occurs only in its natural crystal, the art of working it not having been discovered till comparatively recent times. (The * diamond ' of the High Priest’s breastplate was possibly a white sapphire.) The minerals used belong in the main to a single species known as quartz, and consisting of silica, the oxide of a non-metallic element called silicon. Of these silicious stones there are numberless varieties, differing from one another in texture and colour, and through the presence in small quantities of accessory or intruding materials. Colourless rock-ciystal is the fundamental type of the species. Amethyst differs from it only in its colour, which is generally violet, but sometime citrine, and its curious paiquetted structure. Among the translucent varieties of quartz are the sard. It is the

most beautiful material commonly used for ancient engraved gems, stone amber coloured, red, or reddishbrown ; the less translucent cornelian chalcedony, which is milkv or bhiish, the apple - green chrysoprase, and the leaf green plasma. Jasper, of which there are many varieties, ami which is of very common occurrence, is almost opaque. Another very common stone is the onyx, which is made up of two or more bands of strata, vaiyingin translucency and hue : when one of these strata consists of sard it is called a sardonyx. The sardonyx is fieculiarly interesting from its frequent mention in classical writers. Plato speaks of it. The Romans used it largely, following the fasnion set by the elder Scipio Africanus. Among non-silicious stones are the chrysoberyl, the topaz, the emerald, the almandine and other garnets, the peridot, the turquoise, the opal, and the lapis lazuli (the sap/iints of Pliny the elder).—and these, from the peridot onwards, are softer than quartz, or even than ancient paste or glass. It must be remembered that, for artistic purposes, the most transparent substances, whatever their intrinsic charms, are not necessarily the most beautiful. It is the translucent stones, such as sard and chalcedony, that are more suitable. Through these, light, but not the forms of objects, can be discerned, and so they reveal the charms of fine and noble workmanship more than do the perfectly clear beryl and rock crystal. In the former, the light passes less regular ly—that is, with more scattering of the rays—than is the case with transparent stones, and thus the design seems to be illuminated from within. On the other hand, the opaque substances are less suitable for the purpose. Even such stones as the heliotrope and the turquoise, which are capable, when in thin splinters, of transmitting a little light, produce an effect other and more pleasing than do the perfectly opaque materials. Some of the incident light plunges a little way below the surface of the gem, and lights up its superficial layer. Precious stones, like all other things of value, have been imitated. So we find that many ‘gems,’ as it will be still con venient to call them, have been wrought or reproduced in paste and glass. Paste was a hard glass coloured by various metallic oxides, such as those of man ganese, iron,copper, and cobalt. Sometimes a ptece of paste was treated by the gem-engraver just as if it were a natural stone, and sculptured by the aid of the same tools; but more generally the glass was melted and pressed into a mould. Such amould had been taken front an engraved gent by a pellet of clay which was afterwards hardened by fire. Paste-gems are often of great beauty in colour and design, though the material lacks something of the optical properties which distinguish not a few of the true natural stones. Paste was often legitimately used, but it naturally suggests the subject of fraud. Of jewellers’ frauds, the chief was the making of a * doublet,’ a paste backed with a real stone of greater hardness, but poor colour The two materials were joined by an invisible cement, the line of junction at the girdle of the gem being concealed by the mounting. The alteration and accentuation of the colour of natural stones, particularly of the onyx, by means of various chemicals, is a comparatively recent invention ; but the ancients were adepts in the art of changing the original hue by means of strong heat.