From Agepedia

Jump to: navigation , search

GLASS doubtless owes its origin to chance. Pliny informs vis that Sidon was the first city distinguished for its glassworks, and that the manufacture of glass was not introduced into Rome until the reign of Tiberius. He further states, that, in the reign of Nero, the art of making vases and cups of a white, transparent glass, was invented. De Pau w is of opinion that the Egyptians carried the art to the highest perfection ; and thatthe glassworks at Diospolis, capital of the Thebaid, were the first regular manufactory of this material. The Egyptians, according to the same author, performed the most difficult operations in glasscutting, and manufactured cups of glass of an astonishing purity, of which kind were those called alassontes, supposed to be ornamented with figures in changeable colors. Winckelmann says that the ancients, in general, made much greater use of glass been found in Herculaneum, we find many funeral urns constructed of it. Some of the fragments of cups examined by Winckelmann, appeared to have been cut; some of theraised ornaments having the appearance of being soldered to the surface of the vessels, and bearing marks of the lapidary's wheel on their facettes. The ancients also used glass to ornament their rooms; for this purpose, they employed it of various colors, and composed a sort of mosaic of it. Some blocks,of glass, used for paving rooms, have been found, of the thickness of a common sized brick. Winckelmann cites some specimens of mosaic of remarkable beauty and delicacy. One of them represented a bird on a dark and colored ground. The colors of the bird were very brilliant and various, and the whole effect very soft. The artist had made use of opaque or transparent glass, according to the exigencies of the case. What was not the least remarkable was, that the reverse offered precisely the same figure, without the slightest difference in the details. A little glass ring, which was in the possession of Mr. Hamilton, revealed the method in which this was performed. The exterior of the ring was blue, and the interior represented a species of rose, of different colors, extending the whole circuit of the ring. As melted glass may be drawn out into an amazingly fine wire, this operation may be performed on pieces of glass, compounded of different colors and melted, the colors preserving the respective layers when wiredrawn. Caylus thinks this was the manner in which these works of art were made. The most valuable remains of the ancients, in glass, are the impressions and casts of sculptured gems, both in sunk and raised work, and the larger works in relief, of which one whole vase has come down to us. The glass casts of intaglios often imitate the veins of different colors in the original. These pastes have preserved the impressions of many beautiful gems, which are lost. Of the larger works in relief we have only some fragments: they served as ornaments to the walls of palaces. The most considerable work of this kind is the cameo described by Buonarotti, and preserved in the Vatican: it is an oblong tablet of glass, about 8 inches by 6, representing Bacchus and Ariadne, with two satyrs. But the most beautiful specimens of this art are the vases adorned with figures in relief: they were some, times transparent, sometimes of different tinguished from the vases of sardonyx. The Portland vase is the only one of this sort preserved entire. It was formerly called the Barberini vase, as it belonged to the Barberini palace at Rome. It is about a foot high, and was at first described as a sardonyx. (See Portland Vase.) The ancients were also acquainted with the art of painting on glass (see a subsequent division of this article). Glass is made by melting silicious earth or sand, alkaline substances, and metallic oxide, at a white heat. The name is an old German word, and is connected with gleissen (to shine), and with the English word glisien, and even with glacies (ice) and glanz (splendor). The manufacture of glass is now brought to a high degree of perfection, especially in England. The English glasshouses are commonly large conical buildings, from 60 to 100 feet high, and from 50 to 80 feet in diameter. The furnace is in the middle, over a large vault, which is connected with it by means of an opening. This opening is covered with an iron grate, upon which the fire is made, and it is kept up by the draught of air from the vault. The most important part, however, of the apparatus of the glasshouse, is the crucible.. These instruments are made from a particular kind of clay, which is found at Stourbridge. This is first pounded fine, then sifted, moistened, and worked into a thick dough. Sometimes old crucibles are used, which are broken into powder, and then mixed with a red clay. Some pots, for bottle and flint glass, are made 40 inches deep and wide. They are from two to four inches in thickness. They remain several days at a white heat, before they are placed in the furnace. The basis of glass is silica. Much of the silicious sand used in the U. States comes from the banks of the Delaware. When flints or quartz are used, they are first reduced to powder by being heated red hot, and then plunged into cold water. This causes them to whiten and fall to pieces, after which they are ground and sifted. The second ingredient is an alkaline substance, potash or soda. The alkali used is more or less pure, according to the fineness of the glass to be made. Lime is often employed in small quantities; also borax. Of the metallic oxides added in different cases, the deutoxide of lead is'the'most common. It renders flint glass moie fusible, heavy and tough, and more easy to be ground and cut, increases its brilliancy and glass more transparent; too much gives a purple tinge, which, however, may be destroyed by a little charcoal or wood. Arsenious acid (white arsenic), in small quantities, promotes the clearness of glass; too much of it gives the glass a milky whiteness. Its use in drinlungvessels is not free from danger, if the glass contains so much alkali that any part is soluble in acids. The following are the processes employed in making glass .: Fritting, The various materials are carefully washed, and, after the extraction of all the impurities, are conveyed to the furnace in pots made of tobaccopipe clay* The produce of this process is called the frit, which is again melted in large pots or crucibles, till the whole mass becomes beautifully clear, and the dross rises to the top. Blowing is the next process, which, in round glass, as phials, drinkingglasses, &c, is thus performed : The workmen dip the end of long iron pipes, red hot, into the liquid glass, then roll it on a polished iron plate to give it an external even surface; they next blow down the iron pipe, till it enlarges the metal like a bladder, and, if necessary, roll it again on the iron plate, and proceed to form it into a globular form, or any other one required. The glass is then transferred from the blowing pipe, by dipping the end of another iron rod into the liquid glass, which adheres to the heated rod, and with which the workman sticks it to the bottom of the vessel; then, with a pair of pincers, wetted with water, he touches the neck, which immediately cracks, and, on being slightly struck, separates at the end of the blowingpipe, and becomes attached to the iron rod. The vessel is next carried up to the mouth of the furnace, to be heated and softened, that the operator may finish it. If the vessel require a handle, the operator forms it separately, and unites it while melting hot, forming it with pincers to the requisite shape and pattern.Annealing is the removing of the glass, after it has been blown or cast, into a furnace, whose heat is not sufficiently intense to melt it; and, gradually withdrawing the article from the hottest to a cooler part of the annealing chamber, till it is cold enough to be taken out for use. If cooled too suddenly, it is extremely brittle.Coloring, Tho different colored glasses owe their tints to the different metallic oxides mixed with the materials while in a state of fusion. (See Gems.) In this manner arein brilliancy, their originals, the gems of* antiquity. The glass, however, for this purpose, is prepared in a peculiar manner, and requires great nicety. It combines purity and durability. Opaque glass is made by the addition of the oxide of tin, and produces that beautiful imitation of enamel which is so much admired. Dials for watches and clocks are thus made. The principal sorts of glass are the following : Crown Glass, the beat window glass, is made of white sand, purified barilla, saltpetre, borax and arsenic, melted together ; and, if the glass assume a yellowish hue, the defect is removed by adding a sufficient quantity of manganese. (See Crown GLASS.)Newcastle Glass, generally used in England, is of an ash color, frequently speckled, streaked and blemished. It is made from white sand, unpurified barilla, common salt, arsenic and manganese.The Bottle or Green Glass, usually made of common sand, lime, and some clay, fused with an impure alkali, is very hard, and resists the corrosive action of all liquids much better than flint glass: the green color is owing to the iron: it is well adapted for chemical vessels.Flint Glass, the most fusible of any, is used for bottles, utensils intended to be cut and polished, and for various ornamental purposes. The best kind is composed of white silicious sand, pearlash, red oxide of lead, nitrate of potash, and the black oxide of manganese. It fuses at a lower temperature than crown glass, has a beautiful transparency, a great refractive power, and a comparative softness, which enables it to be cut and polished with ease. On this account it is much used for glass vessels of every description, and especially those which are intended to be ornamented by cutting. It is also employed for lenses and other optical glasses. Flint glass is worked by blowing, moulding, pressing and grinding. Articles of complex form, such as lamps and wineglasses, are formed in pieces, which are afterwards joined by simple contact, while the glass is hot. It appears that the red lead, used in the manufacture of flint glass, gives up a part of its oxygen, and passes to the state of a protoxide.Plate Glassr so called from its being cast in plates or large sheets, is the most valuable, and is used for mirrors and the windows of carriages. It is composed of white sand, cleansed with purified pearlashes and ^borax. But should the metal appear yellow, it is restored to its pellucid transpa and arsenic. It is cast on a large, horizon^ tal table, and all excrescences are pressed out by passing a large roller over the metal. To polish the glass, it is laid on a large, horizontal table of freestone^ perfectly smooth; and then a smaller piece of glass, fastened to a plank of wood, is passed over the other till it has received its due degree of polish. But, to facilitate this process, water and sand are used, as in the polishing of marble; and, lastly, Tripoli stone, smalt and emery, to give it lustre. Grinding and polishing give plate glass a fine lustre. The grinder takes it rough out of the hands of the caster, and, laying it upon a stone table, to which it is fixed with stucco, he lays another rough glass, half the size of the former, upon it. To the smaller glass a plank is fastened, by means of stucco, and to the whole a wheel, made of hard, light wood, about six inches in diameter, by the pulling of which from side to side, and from end to end, of the glass, a constant attrition is kept up ; and, by allowing water and fine sand to pass between the plates, the whole is very finely polished; but to give the finishing polish, powder of smalt is used. As the upper glass grows smoother, it is taken away, and a rougher one substituted in its stead; and so on till the work is done. Except in the very largest plates, the workmen polish their glass by means of a plank, having four wooden handles to move it; and to this plank a plate of glass is cemented, as above. Achromatic Flint Glass, The excise laws of England have prevented English artists from attempting to rnelt glass on a proper scale for making lenses for achromatic telescopes; but in France, where no such restrictions exist, numerous attempts have been made to perfect the manufacture >of flint glass for optical purposes; and M. Guiriaud's labors have been finally crowned With complete success. The almost total impossibility of procuring flint glass exempt from striae, suggested to this artist the construction of a furnace capable of melting two cwt. of glass in one mass, which he sawed vertically, and polished one of the sections, in order to observe what had taken place during fusion. He discovered his metal to be vitiated by striss, specks or grains, with cometic tails; and, from time to time, as he obtained blocks, including portions of good glass, his practice was to separate them by sawing the blocks into horizontal sections, or perpendicular to 43* men were one day carrying a block of this glass, on a hand barrow, to a saw mill which he had erected at the fall of the Doubs, the mass slipped from its bearers, and,' rolling to the bottom of a steep and rocky declivityvwas broken to pieces. M. Guinaud, having selected those fragments Which appeared perfectly homogeneous, softened them, in circular moulds, in such a manner that, on cooling, he obtained disks that were afterwards fit for working. To this method he adhered, and contrived a way of clearing his glass while cooling, so that the fractures should follow the most faulty parts. When flaws occur in the large masses, they are removed by cleaving the pieces with wedges; then melting them again in moulds, which give them the form of disks; taking care to allow a little of the glass to project beyond one of the points of the edge, so that the optician may be enabled to use that portion of glass in making a prism, which shall give the measure of the index of refraction, and thus obviate the necessity of cutting the lens. The astronomical society of London have tried disks of M. Guinaud's flint achromatic glass, which seems entirely homogeneous, and exempt from fault. This material grinds and polishes much easier than the English flint GLASS. Various ornamental forms are given to the surface of glass vessels by metallic moulds. The mould is usually of copper, with the figure cut on its inside, and opens with hinges to permit the glass to be taken out. The mould is filled by a workman, who blows fluid glass into its top. The chilling of the glass, when it comes in contact with the mould, impairs its ductility, and prevents the impression of the figure from being sharp. Some moulds, however, are made in parts, which can be suddenly brought together on the inside and outside of the glass vessel, and produce specimens nearly equal to cut glass.Out Glass, so called, is produced by grinding the surface with small wheels of stone, metal or wood. The glass is held to the surface of the wheels. The first cutting is with wheels of stone ; then with iron, covered with sharp sand or emeiy; and, finally, with brush wheels, covered with putty. A small stream of water is kept continually running on the glass, to prevent the friction from exciting too much heat. The physical properties of glass are of the highest importance. One of these entirely; without extension. Its expansibility is less affected by heat and cold than that of any other solid substance which ftas been accurately examined. On this account, it is especially fit for pendulums. Its great ductility, when heated, is also a remarkable property. It can, in this state, he drawn into all shapes, and even be spun into the finest threads. It may be cut by the diamond, and also by a hot iron, although the last manner is rather unsafe. Drops of Glass, which have been let fall, while melted, into water, commonly called prince RuperVs 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 Galls; a substance which floats upon melted glass, like scum or troth, called by the French siel, or suif de verre. It is principally alkaline, and attracts moisture from the air, so as even to become fluid. It is chiefly used for soldering silver, stands a strong heat, is a good flux for substances difficult to fuse, and keeps them long in a state of fusion. Potters also use it for glazing. Glass Threads. The great ductility of glass enables it to be drawn into the finest threads^ A piece of glass is held over the flame of a lamp, till it becomes soft: a hook is then fixed into it, and it is drawn out into a thread. Tiie 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 JVlndows. The mode of preparing glass was known long before it was mought of making windows of it. Houses in Oriental countries had commonly no windows upon the front, and towards,, the courtyard they were provided with curtains or a movable trelliswork ; and, in winter, they were covered with oiled paper. The Chinese made user for windows, of a very fine cloth, covered with a shining varnish ; and, afterward^ 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 speculaiis supplied the place of glass, and, from the description, seems to have been nothing but thin 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 colored glass in the 4th century after Christ, that is, in the reign of Constantine the Great, when they were to be seen in the church 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 12th 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 1140, by the abbot Suger, a favorite of Louis le Gros. Suger had sapphires pounded up and mixed with the glass, to give it a blue color. ^Eneas Sylvius accounted it one of the most striking instances of splendor which he met in Vienna, in 1458, that most of the houses had glass windows. Felibien says 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 the churches, in the 16th century, although there were but few in dwellinghouses. 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 glassenamel, 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 colored varnishes, as lacker, verdigris, &c, which do not resist moisture. Painting upon glass, properly so called, had its origin in the 3d century, about the time of the first specimens of mosaic. The more exten sive knowledge, as well as use, of colored glass, was communicated from France to England; and from thence, in the 8th century, by means of missionaries, to Germany and Flanders, and, in the 9th 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 8th centuiy. We find undoubtedtraces of it in Bavaria towards the end of <the 1 Oth century. There. was, a glasshouse at Tegernsee, near JYtunich. In the 11th century, the imitation of the best pieces of mosaic work in paintings upon glass was commenced. This, art.derived great advantages^ at the end of the 14th century, from ^he important invention of enamel painting, or the art of fixing the metallic colors in glass. The art flourished most during the 15th and 16th centuries. France, England and the Netherlands boasted firstrate artists in this department, as Henriet, Monier of Blois, and Ab. von Diepenbqcke. In Germany, Diirer gained celebrity in the same art. It declined in the 17th century^ and,,yielding to the force of fashion, it ceased to be heard of in the 18th. It was then chiefly carried on in England,, by foreign artists. In the reign of James I, a school was founded by a jNetherlander, Bernh. de Linge, who, mayhe regarded as the father of modern painting upon glass. . The school has continued to this day. There were, some artists in the 17th and 18th 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 Savior. The. knowledge acquired by experience was not lost, but the practice of the art was very limited. This may be inferred from some treatises Which are extant, as Viel's Art of Painting upon Glass., In Germany, painting upon glass was revived in the 19th centuiy. M. S. Frank, of Nuremburg, first attempted to restore it to its proper rank. He has been em ployed as a painter on glass, at the royal porcelain manufactory at Munich. The royal cabinet of medals possesses a Birth of Christ by him, and the chapel a Supper, which was made in imitation of Diirer's small Passion. (See Speth's paper in the Kunstblatt,,or Journal of Arts, 182(\ No. 27.) The works in painted glass produced at Berlin and Vienna, are not comparable with his. In the castle of Marienburgjin Prussia, recently rebuilt, are some paintings upon glass,which may even be compared to the ancient specimens. Glass is a common term to designate a telescope.. JS/i^Mglass is a telescope made for viewing objects at night. ^ IfalfJiQiir glassy frequently called watch glass, is. used at sea to measure the time which each watch has to stay upon deck To flog or sweat the glass, is to turn it before the sand has quite run out, and thereby, gaining a few minutes each half hour* to make the watch too short. Glass is used in the plural to denote the duration of a naval;action ; as, "They fought yardarm and yardarm three glasses" that is, an hour and a half.