478 



GLASS. 



'snow withdrawn, and squared upon the edges, by 

 being cut with a rouh diamond, and then chipped 

 mi the under side. The plate is now cemented by 

 means of Paris plaster, to a board, and laid horizon- 

 tally \\iili its face uppermost, when another plate 

 similarly fixed is inverted over it. Ground flint and 

 water is placed between them, and the upper plate 

 being set in motion by machinery, the surfaces of 

 both plates are ground plane. The sides are now 

 reversed, and in like manner ground with the flint 

 powder, great care being taken that the plates be 

 made uniformly thick throughout. The same pro- 

 cess is repeated with emery of successive degrees of 

 fineness, after which the plates are examined, and 

 the flaws cut through, forming the sheet into smaller 

 plates. The polishing is then commenced, which is 

 effected by rubbing the plate with a cushion made 

 of Staffed woollen cloth smeared with wetted crocus, 

 or brown-red oxide of iron. 



Drops of Glass, which have been let fall, while 

 melted, into water, commonly called prince Rupert's 

 drops, assume the form of an oval body, terminating 

 in a long slender stem. They are also called glass 

 tears. The large part may be struck with a hammer, 

 or filed, without breaking, but if the stem is broken, 

 the whole flies to pieces. 



Glass Threads. The great ductility of glass en- 

 ables it to be drawn into the finest threads. A piece 

 of glass is held over the flame of a lamp, until it be- 

 comes soft : a hook is then fixed into it, and it is 

 drawn out into a thread. The hook being fixed in 

 the circumference of a small revolving cylinder, the 

 glass thread is wound round the cylinder. Reaumur 

 succeeded in obtaining these threads as fine as a 

 spider's web. 



Glass Windows. The mode of preparing glass 

 was known long before it was thought of making 

 windows of it. Houses in Oriental countries had 

 commonly no windows upon the front, and towards 

 the court-yard they were provided with curtains or a 

 movable trellis-work ; and, in winter, they were cov- 

 ered with oiled paper. The Chinese made use, for 

 windows, of a very fine cloth, covered with a shining 

 varnish ; arid, afterwards, of split oyster shells. 

 They had also the art of working out the horns of' 

 animals into large and thin plates, with which they 

 covered their windows. In Rome, the lapis specu- 

 larig supplied the place of glass, and, from the de- 

 scription, seems to have been nothing but thin 

 leaves of talc. Rich people had the windows or 

 openings in their baths filled with thin plates of 

 agate or marble. It was hastily concluded that 

 glass was used for windows in the time of Titus, 

 because fragments of glass plates have been found 

 at Pompeii, which town was destroyed in his reign ; 

 but the first certain information of this mode of 

 using glass is to be found in Gregory of Tours, who 

 speaks of the churches having windows of coloured 

 glass in the fourth century after Christ, that is, in the 

 reign of Constantine the Great, when they were to 

 be seen in the churcli of St Paolo Fuori le Mura. In 

 France, talc or isinglass, white horn, paper soaked 

 in oil, and thin shaved leather were used instead of 

 glass. The oldest glass windows at present existing 

 are of the twelfth century, and are in the church of St 

 Denis : they appear to have been preserved as part 

 of the old church, which was erected before the year 

 1 140, by the abbot Sugar, a favourite of 'Louis le Gros. 

 Sugar had sapphires pounded up and mixed with the 

 glass, to give it a blue colour. ^Eneas Sylvius 

 accounted it one of the most striking instances of 

 splendour which he met in Vienna, in 1458, that 

 moot of the houses had glass windows. Felibien 

 6ays that, in his time (1600), round glass disks were 

 set in the windows in Italy. In France, on the 



other hand, there were glass windows in all ths 

 churches, in the sixteenth century, although there 

 were but few in dwelling-houses. 



Glass, Painting on. This art was, perhaps, 

 known to the ancients, as Morisoli attempts to prove 

 from passages in Seneca and Vopiscus Firmius ; and 

 some persons consider the fact established by a relic 

 of art, described in Buonarotti's Observations upon 

 some fragments of ancient Vases of Glass, &c. 

 Painted glass was much used, formerly, to ornament 

 windows in churches, and other public buildings, 

 and in unison with the whole style of Gothic 

 churches, throws a gloomy shade over the whole 

 interior. Speth distinguishes between the painting 

 on glass, or glass-enamel, and two inferior kinds of 

 the art ; one painting upon, or rather behind, glass 

 which is not perfectly transparent ; and the other, 

 which requires transparent glass, but makes use only 

 of coloured varnishes, as lacker, verdigris, &c., 

 which do not resist moisture. Painting on glass, 

 properly so called, had its origin in the third cen- 

 tury, about the time of the first specimens of mosaic. 

 The more extensive knowledge, as well as use, of 

 coloured glass, was communicated from France to 

 England ; and from thence, in the eighth century, 

 by means of missionaries, to Germany and Flanders, 

 and, in the ninth century, was carried to the north. 

 Although the Italians used painted glass for mosaic 

 work, yet they appear not to have applied it to 

 church windows before the eight century. We find 

 undoubted traces of it in Bavaria towards the end 

 of the tenth century. There was a glass-house at 

 Tegern-see, near Munich. In the eleventh century, 

 the imitation of the best pieces of mosaic work in 

 paintings upon glass was commenced. This art de- 

 rived great advantages, at the end of the fourteenth 

 century, from the important invention of enamel 

 painting, or the art of fixing the metallic colours in 

 glass. The art flourished most during the fifteenth 

 and sixteenth centuries. France, England, and the 

 Netherlands boasted first-rate artists in this depart- 

 ment, as Henriet, Monier of Blois, and Ab. von Die- 

 penbecke. In Germany, Durer gained celebrity in 

 the same art. It declined in the seventeenth cen- 

 tury, and, yielding to the force of fashion, it ceased 

 to be heard of in the eighteenth. It was then chiefly 

 carried on in England, by foreign artists. In the 

 reign of James I., a school was founded by a Ne- 

 therlander, Bernh. de Lirige, who may be regarded 

 as the father of modern painting upon glass. The 

 school has continued to this day. There were some 

 artists in the seventeenth and eighteenth centuries, 

 who gained reputation by their paintings upon glass, 

 as Eginton of Birmingham, Wolfgang Baumgartner 

 of Kufstein, in the Tyrol (who died 1761), and their 

 contemporary Jouffroy, who painted, in a chapel in 

 London, the resurrection of the Saviour. The know- 

 ledge acquired by experience was not lost, but the 

 practice of the art was very limited. This may be in- 

 ferred from some treatises which are extant, as Viel's 

 Art of Painting upon Glass. In Germany, painting 

 upon glass was revived in the nineteenth century. M. 

 S. Frank, of Nnremburg, first attempted to restore it 

 to its proper rank. He has been employed as a painter 

 on glass at the royal porcelain manufactory at Mu- 

 nich. The royal cabinet of medals possesses a Birth 

 of Christ by him, and the chapel a Supper, which 

 was made in imitation of Dnrer's small Passion. (See 

 Speth 's paper in the Kunstblatt, or Journal of Arts, 

 1820, No. 27.) The works in painted glass produced 

 at Berlin and Vienna, are not comparable with his. 

 In the castle, of Marienburg, in Prussia, recently re- 

 built, are some paintings upon glass, which may even 

 be compared to the ancient specimens. 



Glass is a common term to designate a telescope. 



