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CRYSTALLOGRAPHY
, little need be said here on this subject
.
The brilliancy of a cut See also:
skin
.
This decomposition depends on the dispersive power
of the substance
.
The exceptional beauty of the fiery flashes in the diamond is due to its high See also:dispersion, in other words, to the difference between the refractive indices for the red rays and the See also:violet rays at the extremities of the spectrum
.
The See also:peculiar lustre exhibited by the diamond is called adamantine, and is shared to some extent by certain other stones which have a high refractive index and high dispersion, such as zircon
.
The use of the spectroscope may be valuable in discriminating between certain See also:precious stones
.
It was shown by See also:Sir A
.
H. s ,o, See also: GEMS IN See also:ART fortunately the See also:relief is incomplete, and the published See also:illustration inadequate . It would seem, however, that a revolving See also:tool was supported by a See also:kind of mandrel, and actuated in See also:primitive See also:fashion by a See also:bow . An alternative See also:plan of working was to use a splinter of diamond set in a handle and applied like a graver . Both systems are clearly indicated by See also:Pliny, who in one passage (H.N. See also:xxxvii . 6o) states that diamond splinters are sought out by gem engravers and set in See also:iron, and so easily hollow out stones of any degree of hardness; while elsewhere (H.N. xxxvii . 200) he speaks of the See also:special efficacy of the fervor terebrarum, the vehement See also:action of drills . A third method is also indicated by Pliny (ibid.)' when he speaks of the use of a blunted tool, which must have been moistened and supplied with See also:emery of See also:Naxos . A four-sided See also:pendant of the Hellenistic See also:period published by See also:Furtwangler (Antike Gemmen, Gesch. p . 400) shows clearly the successive stages of the operation . On See also:side a the subject is slightly sketched in with the diamond point . On side b the deepest parts of the figure have also been roughly scooped out with the See also:wheel . On sides c and d the wheel See also:work is fairly See also:complete, but the finer internal work has not been begun . After the See also:design had been completed the stone• must have received a final See also:polish on its See also:surface, to obliterate any erroneous strokes of the first See also:sketch; but this See also:process was not carried as far as in modern work . It is a popular See also:error to suppose that a high degree of internal polish is a See also:proof of antiquity . If the interior of the design has a high degree of polish it may be either See also:ancient or modern, or it may be an ancient stone repolished in modern times . If it has a matt surface uniformly produced by intention, it is probably modern . If the design is slightly dimmed and worn or scratched the stone may be See also:antique, but is not necessarily so, since modern engravers have observed this peculiarity, and have imitated it with a success which, were there no other grounds of suspicion, might See also:escape detection . See also:History.—It has been a subject of controversy whether the first See also:infancy of the art was passed in See also:Egypt or in Babylonia, but it seems highly probable that it was See also:developed in Babylonia, whence at any See also:rate the See also:oldest examples of engraved gems at present known are obtained . It does not necessarily follow, however, that Egypt was therefore a See also:pupil . It may well be that the art was developed independently in the two countries, although certain points of possible contact in respect of the forms employed will be described below in the See also:section dealing with primitive Egypt . Babylonia.—At a very remote period the cylindrical form of stone was introduced and became the approved shape, while the technical skill of the artist was still slight, and the traces of the tools employed (See also:drill and See also:pencil point) were still unconcealed . The See also:cylinder was suspended by a See also:string and used as a See also:seal . Impressions of cylinders are frequent on See also:contract tablets . If one of the parties cannot use a seal he makes a See also:nail-See also:mark in lieu thereof, as is recorded in the document .
But from a See also:time that was still comparatively early the en-gravers could work with considerable skill in the hard stone
.
In particular a cylinder may be quoted in the de Clercq Collection bearing the name of See also:Sargon I. of Agade, who is placed about 3500 B.C
.
The cylinder is engraved with the See also: Apart from workmanship they possess the charms of colour deep, rich, and varied, of material unequalled for its endurance, and of scarcity, which in many instances has been enhanced by the remoteness of the lands whence they came or the fortuity of their occurrence . These qualities See also:united within the small See also:compass of a gem were precisely such as were required in a seal as a thing of See also:constant use, so inalienable in its See also:possession as to become naturally a See also:personal See also:ornament and an attractive See also:medium of artistic skill, no less than the centre of traditions or of religious and legendary associations . As regards the nations of classical antiquity, all See also:seals are classed as gems, though in many cases the material is not such as would strictly come under that heading, and precious stones in the modern sense are hardly known to occur . On the other See also:hand it must not be supposed that gems engraved in intaglio were necessarily employed as seals . At all periods many intaglios are found which could not have been so employed without great difficulty . In See also:Greece and See also:Rome, within historic times, gems were worn engraved with designs to show that the See also:bearer was an adherent of a particular See also:worship, the follower of a certain philosopher, or the attached subject of an See also:emperor . However, speaking generally, the intaglio engraving is a means to an end,. namely, a seal-impression, while an engraving in relief is complete in itself . Methods of Engraving (see also under See also:LAPIDARY).—In gem-engraving the See also:principal modern See also:implement is a wheel or See also:minute See also:copper disk, driven in the manner of a See also:lathe, and moistened with See also:olive oil mixed with emery or diamond dust.' There is no clear proof of the use among the ancients of a wheel mounted lathe-See also:wise, but we have abundant indications of drilling with a revolving tool, which might be either a tubular drill making a See also:ring-like depression, a pointed tool making a See also:cup-like sinking, or a small wheel with a cutting edge, making a See also:boat-shaped depression . We have one sepulchral See also:monument from See also:Philadelphia showing the tool of an intaglio engraver (SaarvXoaOaXoy64os; see Athenische Mitteilungen See also:des See also:Arch . Inst. xv. p . 333) .. Un- form of the conquered, and continued to use it . A Persian cylinder seal of See also:Darius (probably about 500 B.C.) in the British Museum shows the king in his See also:chariot, transfixing a See also:lion with his arrows, in a See also:palm See also:wood . Above is the winged See also:emblem of the Persian deity Ahuramazda . The inscription gives the name and titles of Darius in the Persian, Scythic and Babylonian See also:languages . The style is accurate and minute . The See also:idea of the lion See also:hunt is borrowed from the See also:Assyrian monuments, but the engraver has been careful to make the necessary changes of See also:costume and treatment . The cylinder was, as might be anticipated, imitated to a certain extent by peoples of the Eastern See also:world in See also:touch with Babylonia . It occurs in See also:Armenia, See also:Media and See also:Elam . It has been found in See also:Crete (British School See also:Annual, viii. p . 77) and is frequent in the early Cypriote deposits . In some instances it has been found unfinished and therefore must be supposed to be of See also:local manufacture . Sometimes a See also:direct See also:imitation of See also:cuneiform characters occurs on the Cypriote cylinders . The same form was also employed by the Phoenicians (about the 8th See also:century-7th century B.C.) . By the Greeks and Etruscans it was used, but only rarely, and by way of exception . Egypt.—We must go back to the remotest periods for the origin of intaglio engraving in Egypt . .See also:Recent discoveries of tombs of the earliest dynasties at See also:Abydos and Nagada have thrown much light on the early stages of See also:Egyptian art, and have revealed the remarkable fact that in Egypt (as in Babylonia) the cylinder was the earliest form used for the purpose of a seal . The cylinders that have been found are comparatively few in number; but a large number of See also:jar-stoppings of See also:clay are pre-served on which cylinder designs have been rolled off while the clay was still soft . Such early incised cylinders as are extant are made either of hard wood or (as in an instance in the British Museum) of stone . The identity of form has been thought to indicate a connexion with Babylonia, but none can be traced in the designs of the respective cylinders . The Egyptians of the earliest dynasties had an admirable command of hard stones, as shown by their beads and stone vases, but with the exception of the cylinders quoted they are not known to have applied their skill to the See also:production of intaglios . At this early period the See also:scarab (or See also:beetle) was still unknown as a gem-form . It was only about the time of the 4th See also:dynasty that the scarab (q.v.) was first introduced, and gradually took the See also:place of the cylinder as the prevailing shape . The Scarabaeus sacer (Egyptian, Kheperer), See also:rolling its eggs in a See also:ball of mud, became the accepted emblem of the See also:sun-god, and so the form had an amuletic value . Scarabs of See also:obsidian and crystal date back to the 4th dynasty . Others, coarse 'and uninscribed, belong to the beginning of the first Theban See also:empire . After the 18th dynasty they are counted by thousands . While the beetle form was naturalistically treated, the flat surface underneath .was well adapted to receive a hieroglyphic sign . The scarabs, however, are by no means the only product of the art . We have also figures of all kinds in the See also:round and in intaglio—statuettes, figures of animals and of deities, and sacred emblems such as the ankh (or crux ansata) and the eye . Among interesting See also:variations from the scarab form is the oblong intaglio of green jasper in the Louvre (See also:Gazette arch., 1878, p . 41) with a design on both sides . It represents on the obverse Tethmosis (Thothmes) II . (1800 B.C.) slaying a lion, and identified by his See also:cartouche . On the See also:reverse we have the same king See also:drawing his bow against his enemies from a See also:war chariot . The scarabs of Egypt though uninteresting in themselves, considered as examples of engraving, have this accidental importance in the history of art, that they furnished the Phoenicians with a See also:model which they were able to improve as regards the intaglio by a more See also:free spirit of design, gathered partly from Egypt and partly from See also:Assyria . The scarab thus improved exercised a lasting See also:influence on the later history, since, as will be seen below, it was adopted and modified both by Greeks and Etruscans . Engraved Gems in the See also:Bible.—While the Phoenicians have See also:left actual specimens to show with what skill they could adopt the systems of gem-engraving prevailing at their time in Egypt and Assyria, the Israelites, on the other hand, have left records toprove, if not their skill, at least the estimation in which they held engraved gems . " The sin of See also:Judah is written with a See also:pen of iron and with the point of a diamond " (Jerem. xvii . I) . To See also:pledge his word Judah gave Tamar his signet, with its See also:cord for suspension, and See also:staff (Gen. xxxviii . 18) ; whence if this passage be compared with the frequent use of " seal " in a metaphorical sense in the Bible, and with the usage of the Babylonians of carrying a seal with- an emblem engraved on it recorded by See also:Herodotus, it may be concluded that among the Israelites also every See also:man of mark at least wore a signet . Their acquaintance with the use of seals in Egypt and Assyria is seen in the statement that See also:Pharaoh gave See also:Joseph his signet ring as a badge of See also:investiture (Gen. xli . 42), and that the stone which closed the den of lions was sealed by Darius with his own signet and with the signet of his lords (See also:Daniel vi . 17) . Then as to the stones which were most prized, See also:Ezekiel (See also:xxviii . 13), speaking of the See also:prince of See also:Tyre, mentions " the sardius, the See also:topaz and the diamond, the See also:beryl, the See also:onyx, and the jasper, the See also:sapphire, the See also:emerald and the See also:carbuncle," stones which again occur in that most memorable of records, the description of the breastplate of the high See also:priest (See also:Exodus xxviii . 16-2r, and xxxix . 8-14) . Twelve stones grouped in four rows, each with three specimens, may be arranged on a square, so as to have the rows placed either vertically or horizontally . If they are to See also:cover the whole square, then, unless the See also:gold mounts supplied the necessary See also:compensation, they must be cut in an oblong form, and if the names engraved on them are to run lengthwise, as is the manner of Assyrian cylinders, then the stones, to be legible, must be grouped in four See also:horizontal rows of three each . There is in fact no See also:reason to suppose that the gems of the breastplate were in any other form than that of cylinders such as abounded to the knowledge of the Israelites, with this possibility, however, that they may have been cut lengthways into See also:half-cylinders like a fragmentary one of See also:sard in the British Museum, which has been mounted in See also:bronze, and, as a remarkable exception, has been set with three small precious stones now missing . It could not have been a seal, because of this setting, and because the inscription is not reversed . The names of the twelve tribes, not their See also:standards, as has been thought, may have been engraved in this fashion, just as on the two onyx stones in the preceding verses (Exodus xxviii . 9-11), where there can be no question but that actual names were incised . On these two stones the See also:order of the names was according to See also:primogeniture, and this, it is likely, would apply to the breastplate also . The accompanying See also:diagram will show how the stones, supposing them to have been cylinders or half-cylinders, may have been arranged consistently with th'- descriptions of the See also:Septuagint . In the arrangement of See also:Josephus (iii . 7 . 5) the jasper is made to See also:change places with the sapphire, the amethyst with the See also:agate, and the onyx with the beryl, while our version differs partly in the order and partly in the names of the stones; but probably in all these accounts the names had in some cases other meanings than those which they now carry . It must be remembered that we have two See also:series of equivalents, namely, the See also:Hebrew compared with the Septuagint, and the See also:Greek words of the Septuagint compared with the modern names, which in many cases, though derived from the Greek, have changed their applications . From the fact that to each tribe was assigned a stone of different colour, it may be taken that in each See also:case the colour was one which belonged prescriptively to the tribe and was symbolic, as in Assyria, where the seven See also:planets appropriated each a special colour [see See also:Brandis in See also:Hermes, 1867, p . 259 seq., and de Saulcy, Revue archeologique, 1869, ii. p . 91; and compare See also:Revelation xxi . 12, 13, where the twelve See also:gates, which have the names of the twelve tribes written upon them, are grouped in four threes, and 19, 20, where the twelve precious stones of the walls are given] . The precious stones which occur among the cylinders of the British Museum are sard, emerald, lapis lazuli (sapphire of the ancients), agate, onyx, jasper and See also:rock crystal . Gem-Engraving in Greek Lands.—We must now turn to the history of gem-engraving in Greek lands . The excavations in Crete in the first years of the loth century revealed a previously unknown culture, which lasted on the lowest computation for more than two thousand years, and was only interrupted by the See also:national upheavals which preceded the opening of Greek history proper . (See CRETE; See also:Archaeology; and See also:AEGEAN CIVILIZATION.) Through-out the whole period the products of the gem-engraver occupy an important place among the surviving remains . It must suffice, however, in this place to indicate the See also:chief See also:groups of stones . The earliest engraved stones of Minoan Crete are three-sided See also:prism seals, made of a soft steatite, native in S.E . Crete (Journ. of Hellenic Studies, xvii. p . 328) . These are incised with pictorial signs evidently belonging to a rudimentary hieroglyphic See also:system, and are dated before 3000 B.C . At a period placed by A . J . See also:Evans between 2800 and 2200 the method was fully systematized and employed on the signets, as well as on tablets and other materials . This development of the hieroglyphic system was accompanied by an increasing power of working in hard material, and cornelian and See also:chalcedony superseded soft steatite (Journ. of See also:Hell . Studies, xvii. p . 334) Towards 2000 B.C. a highly developed linear form began to supersede the pictorial signs . It is abundant on the tablets, but the gems thus inscribed are comparatively rare . The linear form in turn died out some six See also:hundred years later . The signs of the pictorial script incised on the gems are re-presentations of See also:objects, expressed with precision, but giving little See also:scope for the higher side of the gem-engraver's art . Simultaneously, however, with the use of the script, a high degree of skill was acquired by the engravers in rendering See also:animal and human forms . Scenes occur of See also:ritual observance, See also:hunting, animal See also:life, and See also:strange compounded forms of demons . The excavations did not yield a large number of original gems of this class, but a great number of clay sealings from such signets were discovered . That they were synchronous with the use of the forms of script described above is proved by the fact that in the See also:palace at See also:Cnossus deposits were found, both in the linear and the hieroglyphic script, sealed with these signets, the seal impressions being again endorsed in the script (Brit . School Annual, xi. pp . 56, 62) . For a remarkable See also:group of sealings found at Zakro see J See also:urn. of Hell . Studies, xxii. p11 . 6-10 . The finest naturalistic engravings are placed towards the See also:close of the " See also:Mid-Minoan " and beginning of the " See also:Late-Minoan " periods (about 2200-1800 B.C.) . During the progress of the " Late-Minoan " period the subjects tended to assume a more formal and heraldic character . The forms of stones in favour were the disk See also:convex on each side (lenticular or lentoid stones), and during the " Mid-Minoan " period, elaborate signets in the form of modern fob-seals . Apart from the use of intaglios for sealing,the excavations have shown that the Cretan lapidaries were largely employed in the working of gems for purposes of decoration . Fragments of lapis lazuli and crystal for See also:inlaying (the crystals having coloured designs on their See also:lower surfaces) were found in the See also:throne See also:room at Cnossus; the royal gaming-See also:board, also from the palace at Cnossus, had inlaid crystal disks and plaques . The workshop of a lapidary, with unfinished See also:works in See also:marble, steatite, jasper and beryl, was also found within the precincts of the palace (Brit . School Annual, vii. pp . 20, 77) . Examples were also found of work in relief, substantially anticipating the art of cameo-cutting . The See also:area over which the Cretan influence extended was wide . Its manifestations in Greek lands proper, first revealed by See also:Schliemann's excavation of the royal tombs of See also:Mycenae, ran parallel with and outlasted the later periods of the Cretan culture to which it stood in close relation (see AEGEAN CIVILIZATION) . Its gems and intaglio works in gold are known to us from the finds at Mycenae, and at analogous sites, such as Menidi, See also:Vaphio and Ialysus . They have much in See also:common with the finer class of Cretan stones already described . The en- i graved gems fall principally into two groups in respect of form, namely, the lenticular (or lentoid) stones already mentioned, and (more rarely) glandular stones, so called from their resemblance to a glans or See also:sling See also:bolt . A Cretan See also:fresco shows a figure wearing an agate lenticular stone suspended from the left See also:wrist . The finer specimens of the Aegean gems are engraved with the wheel and the point in hard stones, such as chalcedony, amethyst, sard, rock-crystal and See also:haematite . A lapidary's workshop similar to that at Cnossus has been found at Mycenae, with a See also:store of unused gems, and an unfinished lenticular stone (See also:Ephemeris Archaiologike, 1897, p . 121) . The characteristic of the Aegean engraver is the free expression of living forms . His subjects are figures of animals, men and demons in combat, and heraldic compositions recalling the See also:Gate of Lions at Mycenae . It was almost inevitable that the scarab should be found in the Cretan and Aegean deposits, but in such cases we have the Egyptian scarab directly imported, and not, as at a later period, non-Egyptian adaptations of the form . The cylinder also (except in See also:Cyprus, the border-See also:land between See also:east and See also:west) only occurs as an importation, and not as a currently manufactured shape . The" See also:Island Gems."—The Aegean culture was swept away probably by that dimly seen upheaval which separated Mycenaean from See also:historical Greece, and which is commonly known as the Dorian invasion . One of the few facts which indicate a certain continuity of tradition in later Greece is this, that we again find the same characteristic forms, the glandular and lenticular stones, in the cemeteries, of Melos and elsewhere . It is only recently that archaeologists have learnt to distinguish between the later lenticular and glandular stones " of the Greek Islands," as they are commonly called, and those of the Aegean See also:age . Engravings of the later class are worked in soft materials only, such as steatite . They have not the power of expressing action peculiar to the Aegean artist . In general, the continuity of tradition between the gems of the Mycenaean and the historical periods is in respect of shape rather than of art . The subjects are for the most See also:part decorative forms (the Gryphon, the winged See also:Sphinx, the winged See also:horse, &c.) in course of development into characters of Greek myth . The Phoenicians and the Greeks.—About the end of the 8th and beginn |