Class XXIV.

WINDOW-GLASS—“CROWN” AND “SHEET” GLASS.

opalescent, imitation of alabaster, gilt, pla-tinised, silvered. i

5. Glass mosaic, millefiori, Aventurine and Yene- !tian glass weights. ,

G. Beads, imitation of pearls, See.

7. Chandeliers, candlesticks, apparatus for lamps.

G. Optical glass, flint and crown. ;

1. Hough discs of flint and crown, to make lenses 1

for telescopes, microscopes, daguerreotype and |calotype apparatus, See. i

2. Flint and crown, blown, or cast in plates for the ■

optician. j

3. Thin glass for microscopes. I

4. Kefractive apparatus, prismatic lenses for light- j

houses.—(See also Class J.) j

Section* A. —TVtWow Glass, $c. |

It bas been observed before, that some degree of un- jcertainty prevails respecting the period when this de- |scripti-on of glass came into general use. It was at first !regarded as an article of luxury and splendour, and 1appears to have been introduced into the churches of 1Francie about the sixth century. Fortunatus of Poitiers , ;who was contemporary with Gregory of Tours , mentionsit in h-is Latin poems, as doing honour to the bishops ofhis day, by whose care the churches had been thus sup-plied with light, and embellished.

According to Bede , artificers skilled in making glasswere invited into England by Abbot Benedict, in theseventh century : and the churches and monasteries ofWearmouth and Yarrow were glazed and adorned by hiscare. Wilfrid, Bishop of Worcester, about the same time,took similar steps for substituting glass in lieu of theheavy shutters which were then in use; and great asto-nishment was excited, and supernatural agency suspected,when the moon and stars were seen through a materialwhich excluded the inclemency of the weather. York Cathedral was glazed about the same time; and in theeleventh aud twelfth centuries, when a great stimulus wasgiven to the erection of religious edifices, glass was gene-rally employed in the windows.

It appears to have been used but very sparingly indomestic architecture till a much later period, when itcame to be gradually adopted in the residences of thewealthy. As late as the middle of the sixteenth century,it wais recommended, in a survey of the Duke of Nor-thumberland's estates, that the glass of the windowsshould be taken down and laid by in safety, during theabsence of the Duke and his family, and be replaced ontheir return, which would be attended with smaller costthan the repair rendered necessary by damage fromweatlher or decay. In Ray’s Itinerary, it is mentionedthat in Scotland , even in 1661, the windows of ordinaryhouses were not glazed, and only those of the principalchambers of the King’s palaces had glass; the lower onesbeing supplied with shutters, to admit light and air atpleasure.

The use of the diamond in glass-cutting, which onlydates from the sixteenth century, greatly facilitated theman ufacture.

There are two methods of making this description ofglass:—

1. By the cylindrical process (sheet-glass).

2. By the effect of centrifugal force (crown-glass).

Ia the first, as soon as the fused metal is in a conditionfor working, a sufficient quantity is collected at the extre-mity* of a pipe, and then lengthened by swinging, andblown at the same time, till it acquires the form of a hol-low globe, or cylinder, open at one end, and adhering tothe mouth of the tube at the other. The cylinder is then !detached from the tube, the neck being cut off with a ;thread of hot glass, and one side of the cylinder is opened :with a heated iron or diamond; after which, it is taken tothe flattening kiln, in which it is heated to softness, and :rubbed down, either upon a stone or upon a sheet of glass,called a largre, by means of a block of wood, called apolissoir. The sheet, thus obtained, is then placed in anannealing kiln, and left there to cool gradually.

By the second operation, the glass collected at the end

of the tube is made to assume the form of a flask, orrounded lump; and then, by a rapid rotary motion, thecentrifugal force causes it to acquire the shape of a largecircular sheet, about at) inches in diameter. The thick-ness of this glass is nearly equal throughout, except atthe knot or bullion, formed at the centre, where the rodor tube was attached to the metal.

The cylindrical process is the only one referred to bythe monk Theophilus, as being in use in his time, whosework, entitled “ Diversorum Artium Scedula,” was writtenabout the end of the twelfth or early in the thirteenthcentury.

This method was principally employed by the Venetians,and was found to possess the advantage of insuring uni-formity of colour in coloured glasses, arising from thegreater equality of their thickness. But as the demandfor coloured glass diminished, the employment of theevlinders was entirely superseded in France . England, andthe north of Germany , by that made on the rotary prin-ciple. It continued, however, to prevail in Bohemia, intowhich country it had been introduced from Venice, andwas carried to so great a degree of perfection that whena glass of large dimensions and good colour was requiredin France , it was imported from Bohemia. In fact, thecircular plates formed by the second process rarely ex-ceeded 3u inches in diameter, and were of such unequalthickness that a square, exceeding 16 inches by 12, couldnot be cut from them.

This state of the manufacture continued till the begin-ning of the eighteenth century, when a French officer,struck with the superiority of the Bohemian glass, formedthe project of introducing this method of fabrication intoFrauce. M. Drolenvaux formed a company for this pur-pose, brought workmen from Bohemia, and established amanufactory at Lettenbach, on the borders of Lorraineand Alsace , in 1730. They carried on their works withso much success, that being unable to purchase the land,which belonged to the monastery of St. Querin, they tookit on lease for 100 years, and it was designated as theManufactory of St. Querin. From this commencementhave sprung all the factories, working glass on the cylin-drical principle, in the Lyonnais , in the north of France ,in Belgium , and latterly in England.

The first workmen, brought over from Bohemia, hadbeen induced to leave their country by the offer of highwages, and fearing a diminution of the advantages whichthey enjoyed, in the event of competition, they enteredinto a combination for confining the business exclusivelyto their own families. They constantly refused to allowstrangers to be taken into the establishment in which theyworked, or even to give them instruction; and if a masterattempted to break through this regulation, the wholeestablishment would throw up their engagements, andleave him unprovided with workmen competent to carryon the busiuess. They thus transmitted their occupationfrom father to son: and the names of Schmidt, Zeller,Theber, Walker, Stenger, Iluy, Mayer, &c., employed inthe manufactories of France , even at the present day,testify their German origin. A similar practice prevailedto a certain degree in England, where the glass-maker’strade is likewise a very exclusive one; and the benefitsocieties, of which the workmen frequently are members,render it exceedingly difficult for the masters, even ifwilling, to depart from ancient practice, and attemptamendments, which are looked upon by the workmenas prejudicial innovations. Another evil of a very seriousnature has also arisen from this system of exclusion,which has been more particularly felt since the alterationof the excise and customs’ duties. This measure, and theconsequent reduction in the price of glass, have caused agreat increase in the demand; and the supply of workmenin this country, properly educated and trained for thenice and difficult process required of them, is so limited,that the manufacturers have found themselves unable toexecute the orders, from want of hands competent tocarry them into execution. Consequently, they havebeen obliged to resort to the Continent, and to bring overworkmen to assist in the works, which can only be accom-plished by means of increased expense in wages.

The great advantage of sheet-glass, obtained by the