vitrum

vī̆trum, i, n. [root in video, to see, as transparent; cf. Plin. 36, 26, 65, § 191], glass.

• I Lit., Plin. 36, 26, 65, § 189; Cic. Rab. Post. 14, 40; Sen. Q. N. 1, 6, 5; Quint. 2, 21, 9; Prop. 4 (5), 8, 37: O fons Bandu siae, splendidior vitro, Hor. C. 3, 13, 1; 1, 18, 16: Bassa, bibis vitro, Mart. 1, 38, 2; Ov. H. 15, 157.—
• II Woad, a plant used for dyeing blue: Isatis tinctoria, Linn.; Vitr. 7, 14; Caes. B. G. 5, 14; Mel. 3, 6, 5; Plin. 35, 6, 27, § 46; 37, 8, 37, § 117.

vitrum, ī, n., I) (ahd. weit) der Waid, eine blaufärbende Pflanze (Isatis tinctoria, L.), Caes. u. Vitr.: auch glastum u. isatis gen., Plin. – II) das Glas, als durchsichtige Masse (s. Plin. 36, 191), vitro similis, Sen.: vitri modo fragilis, Plin.: vitro inclusus, in einem verschlossenen Glase, Plin.: merces in chartis et linteis et vitro delatae, Cic.: vitrum conflare, Glasmacher sein, Vopisc.: vitrum solvere formareque, Macr.: vitrum fundere, Plin.: vitro absconditur camera, ist mit Gl. überzogen, Sen. – vitrum ruptum, Glasscherbe, Iuven. 5, 46.

1 vitrum [CL], glass. b pane of glass, glass window. c glass vessel. sicut in vitreo vasculo lux intus absconditur, et foras per ~um refulget Alcuin Dogm. 296A; albo ~o, quod quia rarum et lucidum est, penetrari a tali spiritu potest Adel. QN 29; ex favilla vili fiat materia quae sit solida ac visu penetrabilis visuique jocunda, utpote ~um Alex. Cant. Dicta 124; inter inanimata ‥ quid fragilius est ~o? Bern. Comm. Aen. 29; 1240 duas fenestras de albo ~o ‥ facias Liberate 15 m. 23; sicut lux pertransiens ~um coloratum colorat parietem objectum, et immediatius splendet in pariete quam color ~i Gros. Quaest. Theol. 205; 1291 appellat R. C. ‥ de quadam roberia ‥ ut de denariis, ciphis argenti et de vuitro et aliis jocalibus et equis SelCCoron 127; vas istud adeo fragile est ut ~um [ME: gles] AncrR 54; 1388 vitriario pro viij pedibus ~i flor' et partim depict' emptis pro defectibus diversarum fenestrarum in camera et capella regis ibidem emendandis KR Ac 473/2 m. 5.  b 1274 una camera magna cum aluris et ~is IPM 2/7 m. 7; mare apparuit eis quasi ~um unum valde clarum, ita ut viderent profunda maris (Brendanus 56) VSH I 128.  c spiritus ergo viri Michael repetente beati, / vimineo condens corpus kiriale canistro, / exhausit vitro vitalem digne cruorem Frith. 1357; ‘~o’, vase vitreo Andr. S. Vict. Sal. 72; mors ridet medicum qui vitro medio / morbum in morbidi venatur locio Walt. Wimb. Sim. 197; caveas in omni sublimacione a fractione ~i aut tui vasis Dastin Ros. 9; 1418 quandam materiam nigram confecit ‥ existentem arsam et congellatam in quodam ~o rotundo CoramR 629 rex r. 18d.; in uno ~o debent omnia fieri, ovo simili in forma et bene clauso Ripley Axiom. 112.

2 vitrum [CL], woad (Isatis tinctoria) or the blue dye derived from its leaves. 1296 de R. C. quia vendit ~um mixtum cum vertegrez et arguel mixtum cum fecibus vini Leet Norw. 47; 1398 in uno panno serico cum duabus peciis de bucram ‥ et duobus duodenis de zonis xlj s. iiij d. item in centum libris ~i Anglicani empt', xxx s. Ac. Durh. 393.

vĭtrum, (12) ī, n. , ¶ 1 verre : Cic. Rab. Post. 40 ; Hor. O. 3, 13, 1 ; Sen. Nat. 1, 6, 5 ¶ 2 pastel ou guède, plante donnant une couleur bleue : Cæs. G. 5, 14, 2 ; Vitr. Arch. 7, 14 ; Plin. 35, 46.

vitrum , i. n.
染靑色之草。玻璃。

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vitrum ī, n

• VID-, glass: fons splendidior vitro, H., C., O.—A blue vegetable dye, woad: se Britanni vitro inficiunt, Cs.

VITRUM

VITRUM(ὕαλος), glass. A singular amount of ignorance and scepticism long prevailed with regard to the knowledge possessed by the ancients in the art of glass-making. Some asserted that it was to be regarded as exclusively a modern invention, while others, unable altogether to resist the mass of evidence to the contrary, contented themselves with believing that the substance was known only in its coarsest and rudest form. It is now clearly demonstrated to have been in common use at a very remote epoch. Various specimens still in existence prove that the manufacture had in some branches reached a point of perfection to which recent skill has not yet been able to attain; and although we may not feel disposed to go so far as Winckelmann (1.100.2.20), who contends that it was used more generally and for a greater variety of purposes in the old world than among ourselves, yet when we examine the numerous collections arranged in all great public museums, we must feel convinced that it was employed as an ordinary material for all manner of domestic utensils by the Egyptians, Greeks, and Romans.

A vitreous glaze is found in remains dating from the earliest periods of Egyptian history, and we find the process of glass-blowing distinctly represented in the paintings of Beni-Hassan, which were executed during the reigns of Usertesen the First and his immediate successors (circa 2300 B.C.). The oldest Egyptian glass proper which can be dated with certainty is a vase of opaque blue glass in the British Museum, with a design inlaid in yellow, which includes the name of Thothmes II. (16th cent. B.C.). Vases also, wine-bottles, drinking-cups, bugles, and a multitude of other objects have been discovered in sepulchres and attached to mummies both in Upper and Lower Egypt; and although in most cases no precise date can be affixed to these relics, many of them are referred to an early period. (Wilkinson, Ancient Egyptians, iii.3 pp. 141 f.; Deville, L'Art de la Verrerie, pl. iii.)

The Assyrians also attained to a high degree of skill in glass-making. The oldest piece with a fixed date is an alabastron of bright green glass from the North-west Palace at Nimroud, with the name of king Sargon, B.C. 719 (Layard, Nineveh and Babylon, p. 197; Froehner, La Verrerie ant. p. 16). This vase is in the British Museum.

A story has been preserved by Pliny (Plin. Nat.36.191), that glass was first discovered accidentally by some merchants who having landed on the Syrian coast at the mouth of the river Belus, and being unable to find stones to support their cooking-pots, fetched for this purpose from their ship some of the lumps of nitre which composed the cargo. This being fused by the heat of the fire, united with the sand upon which it rested and formed a stream of vitrified matter. The Phoenicians probably learnt the art of glass-making from the Egyptians; but the tale is no doubt connected with the fact recorded by Strabo (16. p. 758) and Josephus (B. J. 2.9), that the sand of the district in question was esteemed peculiarly suitable for glass-making, and exported in great quantities to the workshops of Sidon, long the most famous in the ancient world. (See Hamburger and Michaelis on the Glass of the Hebrews and Phoenicians, Commentar. Soc. Gott. vol. iv.; Heeren, Ideen, 1. p. 94.) Alexandria, another centre of the industry, sustained its reputation for many centuries; Rome derived thence a great portion of its supplies, and as late as the reign of Aurelian we find the manufacture still flourishing (Cic. pro Rabir. Post. 14, 40; Strabo, l. c.; Martial (Mart. 11.11, 12.74-Z2, 14.115-Z2; Vopisc. Aurel. 45; Boudet, Sur l'Art de la Verrerie né en Egypte; Description de l'Egypte, vol. 9. p. 213).

Glass is not mentioned in Homer, unless Helbig's theory is accepted that κύανος is a blue vitreous glaze (Helbig, Homerisches Epos, p. 80). In the deposits of Mycenae and kindred sites, numerous beads, rosettes, pendants, and other ornaments of glass occur. Bottles, however, are very rare; a few only having been found at Ialysos in Rhodes.

There is some difficulty in deciding by what Greek author glass is first mentioned, because the term ὕαλος, like the Hebrew word used in the Book of Job (28.17) and translated in the LXX. by ὕαλος, unquestionably denotes not only artificial glass but rock-crystal, or indeed any transparent stone or stone-like substance (Schol. ad Aristoph. Nub. 768). Thus the ὕελος of Herodotus (Hdt. 3.24), in which the Ethiopians encased the bodies of their dead, cannot be glass, although understood in this sense by Ctesias and Diodorus (Diod. 3.15), for we are expressly told that it was dug in abundance out of the earth; and hence commentators have conjectured that rockcrystal or rock-salt, or amber, or Oriental alabaster, or some bituminous or gummy product, might be indicated. But when the same historian in his account of sacred crocodiles (2.69) states that they were decorated with ear-rings made of melted stone (ἀρτήματά τε λίθινα χυτὰ καὶ χρύσεα ἐς τὰ ὦτα ἐνθέντες, we may safely conclude that he intends to describe some vitreous ornament for which he knew no appropriate name. The σφραγὶς ὑαλίνη and σφραγῖδε ὑαλίνα of an Athenian inscription referred to B.C. 398 (Boeckh, Corp. Inscr. Gr. n. 150.50), together with the passage in Aristophanes (Acharn. 74) where the envoy boasts that he had been drinking with the Great King ἐξ ὑαλίνων ἐκπωμάτων, are not decisive. But the early Greek pastes with designs in intaglio, preserved in all museums, make it highly probable that the seals referred to above were of glass. Vessels of glass also appear to be mentioned in the treasure lists at the beginning of the 4th century (C. I. A. 2.645, 646, 656). Setting aside the two problems with regard to glass, attributed to Aristotle, as confessedly spurious, we at length find a satisfactory testimony in the works of his pupil and successor, Theophrastus, who notices the circumstances alluded to above, of the fitness of the sand at the mouth of the river Belus for the fabrication of glass. Blümner, however (Technologie, 4. p. 384), questions whether glass was manufactured in Greece itself, even in the time of the Diadochi.

Among the Latin writers Lucretius appears to be the first in whom the word vitrum occurs (4.604, 6.991); but it must have been well known to his countrymen long before, for Cicero names it, along with paper and linen, as a common article of merchandise brought from Egypt (pro Rab. Post. 14, 40). Glass of Phoenician importation occurs indeed in cemeteries of the 8th century, at Tarquinii (Helbig, Homerisches Epos, p. 15). Scaurus, in his aedileship (B.C. 58), made a display of it such as was never witnessed even in after-times; for the scena of his gorgeous theatre was divided into three tiers, of which the under portion was of marble, the upper of gilded wood, and the middle compartment of glass (Plin. Nat.36. § § 114, 189). In the poets of the Augustan age it is constantly introduced, both directly and in similes, and in such terms as to prove that it was an object with which every one must be familiar (e. g. Verg. G. 4.350, Aen. 7.759; Ovid, Amor. 1.6, 55; Prop. 4.8, 37; Hor. Carm. 3.13, 1). Strabo declares that in his day a small drinking-cup of glass might be purchased at Rome for half an as (16. p. 758; compare Martial (Mart. 9.60), and so common was it in the time of Juvenal and Martial, that old men and women made a livelihood by bartering sulphur matches for broken fragments (Juven. 5.48; Martial (Mart. 1.42, 10.3-Z2; Stat. Sylv. 1.6, 73; compare Dio Cass.). When Pliny wrote, manufactories had been established not only in Italy, but in Spain and Gaul also, and glass drinking-cups had entirely superseded those of gold and silver (H. N. 36. § § 192-199), and in the reign of Alexander Severus we find vitrearii ranked along with curriers, coachmakers, goldsmiths, silversmiths, and other ordinary artificers whom the emperor taxed to raise money for his thermae (Lamprid. Alex. Sev. 24). A list of the glass-workers whose names are known as occurring on extant specimens, is given by Froehner, La Verrerie antique, p. 123.

The numerous specimens transmitted to us prove that the ancients were well acquainted with the art of imparting a great variety of colours to their glass; they were probably less successful in their attempts to render it perfectly pure and free from all colour, since we are told by Pliny that it was considered most valuable in this state. It was wrought according to the different methods now practised, being fashioned into the required shape by the blowpipe; or cut, as we term it, although ground (teritur) is a more accurate phrase, upon a wheel; or engraved with a sharp tool, like silver ( aliud flatu figuratur, aliud torno teritur, aliud argenti modo caelatur, Plin. Nat.36.193). The diatreta of Martial (Mart. 12.70) were glass cups cut or engraved according to one or other of the above methods. The process was difficult, and accidents occurred so frequently (Mart. 14.115) that the jurists found it necessary to define accurately the circumstances under which the workman became liable for the value of the vessel destroyed (Dig. 9, 2, 27, 29). The art of etching upon glass, now so common, was entirely unknown, since it depends upon the properties of fluoric acid, a chemical discovery of the last century.

We may now briefly enumerate the chief uses to which glass was applied. The best idea, however, of the admirable ingenuity and skill of the ancient glass-workers, may be obtained from such a collection as that of the British Museum, or the chief continental cabinets. Specimens of the different types are finely engraved by Froehner, La Verrerie antique(1879).

1. Bottles, vases, cups, and cinerary urns. These specimens are extant in immense number and variety. Many which have been shaped by the blowpipe only, are remarkable for their graceful form and brilliant colours. Some have been blown out into moulds, by the blow-pipe, and appear in the form of a bunch of grapes (cf. Achilles Tatius, 2, 3), a shell, or a negro's head. Others are of the most delicate and complicated workmanship. A very remarkable object belonging to the last class, now in the Trivulsi Collection at Milan, is described in the notes to Winckelmann (1.100.2.21) and figured in Vol. I. under DIATRETAThat woodcut, however, hardly does justice to the delicacy of the work, which is better shown in the photographic plate of Adda, Ricerche sulle Artie sull' Industria Romana. For a description, see DIATRETAVol. I., p. 626. A small fragment of a similar vase may be seen in the glass collection of the British Museum. Another cup, found at Strasburg, was dated by the name of the Emperor Maximian (286-310. A.D.). This specimen, which perished in 1870, is engraved by Deville, L'Art de la Verrerie, pi. xxxiii A. But the great triumph of ancient genius in this department is the celebrated Port-land Vase, formerly known as the Barberini Vase, which is now in the British Museum. It was found in the 16th century at a short distance from Rome, in a marble coffin within a sepulchral vault, pronounced upon very imperfect evidence to have been the tomb of Alexander Severus. The extreme beauty of this urn led Montfaucon and other antiquaries to mistake it for a real sardonyx. Upon more accurate examination it was ascertained to be composed of dark blue glass, of a very rich tint, on the surface of which are delineated in relief elaborately wrought figures of opaque white glass. [See SCALPTURA] With such samples before us, we need not wonder that in the time of Nero a pair of moderate-sized glass cups with handles (pteroti) sometimes cost fifty pounds (HS. sex millibus,Plin. Nat.36.195). Another method practised with success was that of adding coloured glasses in a fused state to a background, in the manner of enamel. See a medallion with a gryphon, now in the British Museum (Catalogue of the Slade Collection, No. 84).

2. Glass Pastes presenting fac-similes, either in relief or intaglio, of engraved precious stones. In this way have been preserved exact copies of many beautiful gems, of which the originals no longer exist, as may be seen from the catalogues of Stosch, of Tassie, and from similar publications. These were in demand for the rings of such persons as were not wealthy enough to purchase real stones, as we perceive from the phrase vitreis gemmis ex vulgi anulis (Plin. Nat.35.48). Large medallions also of this kind are still preserved, and bas-reliefs of considerable magnitude, which successfully imitate precious materials, and in some cases the true material has only been ascertained in quite recent years. (See Winckelmann, 1.100.2.27.)

3. Closely allied to the preceding were imitations of coloured precious stones, such as the carbuncle, the sapphire, the amethyst, and, above all, the emerald. These counterfeits were executed with such fidelity that detection was extremely difficult, and great profits were realised by dishonest dealers who entrapped the unwary (Plin. Nat.37.197). That such frauds were practised even upon the most exalted in station is seen from the anecdote given by Trebellius Pollio of the whimsical vengeance taken by Gallienus (Gall. 100.12) on a rogue who had cheated him in this way, and collections are to be seen at Rome of pieces of coloured glass which were evidently once worn as jewels, from which they cannot be distinguished by the eye. (Plin. Nat.37.98; Senec. Ep. 90; Isidor. Orig. 16.15.27; Beckmann, History of Inventions, vol. 1. p. 199, Eng. Trans. 3rd edit.)

4. One very elegant application of glass deserves to be particularly noticed. A number of fine stalks of glass of different colours were placed vertically, and arranged in such a manner as to depict upon the upper surface some figure or pattern, upon the principle of a minute mosaic. The filaments thus combined were then subjected to such a degree of heat as would suffice to soften without melting them, and were thus cemented together into a solid mass. It is evident that the picture brought out upon the upper surface would extend down through the whole of the little column thus formed, and hence, if it was cut into thin slices at right angles to the direction of the fibres, each of these sections would upon both sides represent the design which would be multiplied to an extent in proportion to the total length of the glass threads. Further, if the column is heated and drawn out, the design becomes proportionately minute. When these sections have been again fused together side by side, the result is millefiori glass (Cat. of the Slade Collection, pl. iv.). Two beautiful fragments evidently constructed in this way are accurately commented upon by Winckelmann (1.100.2, § § 22-24); another, more recently brought from Egypt, is shown in Wilkinson's work, Pl. xiv., figs. 5, 6, 7; cf. vol. 2. p. 146. Many mosaic pavements and pictures (opus musivum) belong to this head, since the cubes were frequently composed of opaque glass as well as marble, but these have been already discussed under PICTURApp. 397 f.

5. One method of decoration employed by the ancients consisted in enclosing designs in gold leaf between two layers of transparent glass. This is most common from the 3rd century A.D., when small Christian subjects are thus represented. Examples also occur of a good Greek period, such as three cups from Canosa, now in the British Museum, perhaps dating from 200 B.C., but these are very rare. The Christian examples have been described by Garrucci, Vetri ornati di Figure in oro dei Cristiani. In a few rare examples, the gold leaf has been cut away with a sharp point, in such a way as to produce the effect of a finely-stippled drawing.

6. Thick sheets of glass of various colours appear to have been laid down for paving floors, and to have been attached as a lining to the walls and ceilings of apartments in dwelling-houses, just as scagliola is frequently employed in Italy, and occasionally in our own country also. Rooms fitted up in this way were called vitreae camerae, and the panels vitreae quadraturae. Such was the kind of decoration introduced by Scaurus for the scene of his theatre, not columns nor pillars of glass as some, nor bas-reliefs as others, have imagined. (Plin. Nat.36.189; Stat. Syl. 1.5, 42; Senec. Ep. 76; Vopisc. Firm. 100.3; Winckelmann, 1.100.2.21; Passeri, Lucernae Fictiles, p. 67, tab. lxxi.)

7. The question whether glass windows were known to the ancients has, after much discussion, been set at rest by the excavations at Pompeii, for not only have many fragments of flat glass been disinterred from time to time, but in the tepidarium of the public baths a bronze lattice came to light with some of the panes still inserted in the frame, so as to determine at once not only their existence, but the mode in which they were secured and arranged. (Mazois, Palais de Scaurus, c. viii. p. 97; Rusines de Pompéi, vol. 3. p. 77.) A few specimens of window glass may be seen in the glass collection of the British Museum. [DOMUSVol. 1. p. 686 b. ] The same collection also contains a wooden picture-frame of late Graeco-Egyptian origin, with a rebate for a sheet of glass. (Petrie, Hawara, pl. xii.)

8. From the time that pure glass became known, it must have been remarked that when darkened upon one side, it possessed the property of reflecting images. We are certain that an attempt was made by the Sidonians to make looking-glasses (Plin. Nat.36.193), and equally certain that it must have failed, for the use of metallic mirrors, which are more costly in the first instance, which require constant care and attain but imperfectly the end desired, was universal under the Empire. Respecting ancient mirrors, see SPECULUM

9. A strange story with regard to an alleged invention of malleable glass is found in Petronius (100.51), is told still more circumstantially by Dio Cassius (Dio Cass. 57.21), and is alluded to by Pliny (Plin. Nat.37.195), with an expression of doubt as to its truth. An artist appeared before Tiberius with a cup of glass. This he dashed violently upon the ground. When taken up, it was neither broken nor cracked, but dinted like a piece of metal. The man then produced a mallet, and hammered it back into its original shape. The emperor inquired whether any one was acquainted with the secret, and was answered in the negative, upon which the order was given that he should be instantly beheaded, lest the precious metals might lose their value, should such a composition become generally known.

Literature.--Franks in Art Treasures of the Manchester Exhibition Section Vitreous Art; Nesbitt, Catalogue of the Slade Collection of Glass, Notes on the History of Glass-making (1871); Blümner, Technologie, 4. p. 379; Deville, Hist. de l'Art de la Verrerie, 1873; Froehner, La Verrerie antique, 1879; Marquardt and Mommsen, Handb. d. römischen Alterthümer, vol. vii. (1886), p. 744. References to the older literature may be found in the above works.

[W.R] [A.H.S]

Vitrum

(ὕαλος). Glass. The Egyptians made glass at a very early period, the oldest existing specimen being a blue vase of opaque glass now in the British Museum, as old as the sixteenth century B.C. Cups and bottles of uncertain date have been taken in considerable numbers from the tombs and mummy-cases. In the paintings of Beni-Hassan (about 2300 B.C.) the process of glass-blowing is clearly depicted. The Assyrians likewise made admirable glass, the oldest existing specimen being a sort of bottle of green glass found at Nimroud, and dating from 719 B.C. It is now in the British Museum.

A story has been preserved by Pliny (Pliny H. N. xxxvi. 191) that glass was first discovered accidentally by some merchants who, having landed on the Syrian coast at the mouth of the river Belus, and being unable to find stones to support their cooking-pots, brought for this purpose from their ship some of the lumps of nitre which composed the cargo. This being fused by the heat of the fire, united with the sand upon which it rested and formed a stream of vitrified matter. The Phoenicians probably learned the art of glass-making from the Egyptians; but the tale is no doubt connected with the fact recorded by Strabo (xvi. p. 758) and Iosephus (Bell. Iud. ii. 9), that the sand of the district in question was esteemed peculiarly suitable for glass-making, and exported in great quantities to the workshops of Sidon, long the most famous in the ancient world. Alexandria, another centre of the industry, sustained its reputation for many centuries; Rome derived thence a great portion of its supplies, and as late as the reign of Aurelian we find the manufacture still flourishing (Cic. Pro Rabir. Post. xiv. 40; Strabo, l. c.; Martial, xi. 11; xii. 74; xiv. 115; Vopisc. Aurel. 45).

Homer does not certainly mention glass, but at Mycenae and Tiryns glass beads and other ornaments have been found. The words ὕαλος and ὕελος in the early Greek writers (e. g. Herod. iii. 24) do not always refer to glass, but often to rockcrystal, rock-salt, amber, or alabaster; and it is not till Theophrastus, the pupil of Aristotle, that the word is surely to be rendered “glass.” Of the Roman writers, Lucretius is the first to use the term vitrum (iv. 604; vi. 991), but it must have been known at Rome long before this time, as Cicero (l. c.) speaks of it as a common article of merchandise. Phoenician glass is found in the Etruscan cemeteries at Tarquinii dating from the eighth century B.C. Scaurus in his temporary theatre, erected in B.C. 58, used glass freely in the interior decoration (see theatrum); and the Augustan poets often mention the substance (e. g. Verg. Georg. iv. 350; Aen. vii. 759; Ovid, Amor. i. 6, 55; Hor. Carm. iii. 13. 1). Pliny states that glass was made in Italy, Gaul, and Spain, and that drinking-cups of glass had superseded those of gold and silver (Pliny H. N. xxxvi. 192-199). Under Alexander Severus we find the glass-makers (vitrearii) enumerated in the tax-lists with other artisans. Strabo notes the cheapness of glass, and says that a glass drinking-cup sold in his time for half an as, or less than a cent.

The following are the chief uses to which glass was applied:

(a) Bottles, vases, cups, and urns for the ashes of the dead (cineraria). Of all of these great numbers exist, in a great variety of forms and colours, some having been blown into moulds so as to take the shape of—e. g. a bunch of grapes, a sea-shell, a negro's head, etc. (See illustration, s. v. diatreta.) The finest of all under this class is the celebrated Portland Vase in the British Museum, found in the sixteenth century near Rome. See Portland Vase.

(b) Glass pastes giving fac-similes of engraved precious stones. These were worn by those who could not afford real gems (Pliny H. N. xxxv. 48). Precious stones were also imitated in glass with very great skill, so that only experts could detect the imposition. The sapphire, amethyst, carbuncle, and especially the emerald, were the oftenest counterfeited (Pliny H. N. xxxvii. 197; Trebell. Poll. Gall. 12; Seneca, Epist. 90; Isidor. Orig. xvi. 15, 27). See gemma.

(c) One very elegant application of glass deserves to be particularly noticed. A number of fine stalks of glass of different colours were placed vertically, and arranged in such a manner as to depict upon the upper surface some figure or pattern, upon the principle of a minute mosaic. The filaments thus combined were then subjected to such a degree of heat as would suffice to soften without melting them, and were thus cemented together into a solid mass. It is evident that the picture brought out upon the upper surface would extend down through the whole of the little column thus formed, and hence, if it was cut into thin slices at right angles to the direction of the fibres, each of these sections would upon both sides represent the design which would be multiplied to an extent in proportion to the total length of the glass threads. Further, if the column is heated and drawn out, the design becomes proportionately minute. When these sections have been again fused together side by side, the result is millefiori glass. Many mosaic pavements and pictures (opus musivum) belong to this head, since the cubes were frequently composed of opaque glass as well as marble. See musivum opus.

(d) One method of decoration employed by the ancients consisted in enclosing designs in gold-leaf between two layers of transparent glass. This is most common from the third century A.D., when small Christian subjects are thus represented.

(e) Thick sheets of glass of various colours appear to have been laid down for paving floors, and to have been attached as a lining to the walls and ceilings of apartments in dwelling-houses, just as scagliola is frequently employed in Italy. Rooms fitted up in this way were called vitreae camerae, and the panels vitreae quadraturae. Such was the kind of decoration introduced by Scaurus for the scene of his theatre, not columns nor pillars of glass as some, nor bas-reliefs as others, have imagined (Pliny H. N. xxxvi. 189; Stat. Sil. i. 5, 42; Sen. Ep. 76; Vopisc. Firm. 3).

(f) The question whether glass windows were known to the ancients has, after much discussion, been set at rest by the excavations at Pompeii, for not only have many fragments of flat glass been disinterred from time to time, but in the tepidarium of the public baths a bronze lattice came to light with some of the panes still inserted in the frame, so as to determine at once not only their existence, but the mode in which they were secured and arranged (Mazois, Ruines de Pompéi, iii. p. 77).

For the use of glass in mirrors, see speculum.

The numerous specimens existing prove that the ancients were well acquainted with the art of imparting a great variety of colours to their glass; they were probably less successful in their attempts to render it perfectly pure and free from all colour, since we are told by Pliny that it was considered most valuable in this state. It was wrought according to the different methods now practised, being fashioned into the required shape by the blowpipe; or cut, as we term it, although “ground” (teritur) is a more accurate phrase, upon a wheel; or engraved with a sharp tool, like silver (Pliny H. N. xxxvi. 193). The process was difficult, and accidents occurred frequently (Mart. xiv. 115). The art of etching upon glass, now so common, was entirely unknown to the ancients, since it depends upon the properties of fluoric acid, a chemical discovery of the last century.

Petronius and Dio Cassius assert that malleable glass was discovered in the reign of the emperor Tiberius. They tell a story of how a man demanded an interview with the emperor, and, on being admitted, showed him a glass vessel and then dashed it violently upon the ground. When taken up, it was neither broken nor cracked, but dinted like a piece of metal. The man then produced a mallet, and hammered it back into its original shape. The emperor inquired whether any one was acquainted with the secret, and was answered in the negative; upon which the order was given that the man should be instantly beheaded, lest the precious metals might lose their value, should such a composition become generally known.

See Nesbitt, Notes on the History of Glass-making (1871); Blümner, Technologie, iv. p. 379 (1887); Deville, Histoire de l'Art de la Verrerie (1873); Fröhner, La Verrerie Antique (1879); Beckmann, History of Inventions (1856); Marquardt and Mommsen, Röm. Alterthümer, vii. pp. 774 foll. (1886).