About the end of the 3(1 century, as appears from a passage in Lactantius,* glass was used for windows ; and there is reason to believe, from the glass plates found in Herculaneum, that window glass had been introduced at a much earlier period. St Jerome, A. D. 422, Paulus Si lcntiarus, A. D. 534, Gregory of Tours, A. D. 571, and Johannes Philoponus, A. D. 6304 all speak in the most distinct manner of the use of glass in the Formation of windows.
Italy was the first modern nation that employed glass in windows. The custom was afterwards introduced ilto France; and though the art of making glass was brought into England in A. D. 674, by foreign artists sent for by the Abbot Benedict, who glazed the church and monas tery of Weremouth in Durham, yet this great invention was so much neglected, that private houses were not light ed through glass till the end of the 10th century. The windows of houses, and even the cathedral churches, were covered with fine linen cloths.
The application of painted glass to the decoration of church windows, was made before the commencement of the 9th century, as we are informed by Anastasius, libra rian to Pope Leo III. that painted glass was used in his time. This art made rapid advances to perfection ; and all the ingenuity of the art was exhausted in the produc tion of those splendid windows which at present adorn the Gothic cathedrals of Europe. The al t of staining glass, though still known and practised, is, however, to a cer tain extent lost ; and we admire, without being able to imi tate, some of the rich productions of the middle ages. We have had occasion to see a specimen of glass, brought home by Dr Brewster from the abbey of Konigsfeld, in Switzerland, which consists of six different layers of green and purple glass placed alternately. The thickness of the plate is only about the seventh part of an inch ; and the different layers have an equality of thickness, and a paral lelism, which is truly surprising. The compound colour is a light purple. section of this plate is shewn in Plate CCLXXV. Fig. 5, the dark layer representing the purple, and the light one the green glass.
The art of making plate glass by blowing, was carried on to a great extent at the village of Murano, near Venice ; and Europe was long supplied from this quarter with the finest and largest mirrors.
Vie are indebted, however, to the French, for the art of casting large plates or glass, which was introduced in 1688 by Abraham Thevenart. An account of this establish ment, and of the glass manufactories in England, will be found in our articles ENGLAND, and FRANCE.
Glass appears to have been first made in Scotland in the reign of James VI. and the exclusive right of manu facturing it within the kingdom, was given to Lord George Hay for 31 years, from 1610. This right was transferred in 1627 for a considerable sum, to Thomas Robinson, mer chant•tailor in London, who again transferred it for 250/. to Sir Robert Mansell, vice-admiral of England. A manu factory of glass was carried on for some time in a cave at \Vemyss, in Fifeshire. Regular glass works were after wards established at Prestonpans ; hut the principal places where glass is now made in Scotland, are Lcith,f Glasgow, and Dumbarton.
The glasshouses now in use are commonly large cones, from 60 to 100 feet high, and from 50 to 80 feet in diame ter at the base. The ,furnace is erected in the centre, over a large vault, that extends from one side of the cone to the other. The vault or cave is generally made of a sufficient height and width to allow the workmen to wheel a barrow with rubbish out and in. This, however, is not the only purpose of this cave, as it is made to communicate wi,h the furnace by an aperture in the top of it, of such a size as the furnace above may require. Over this aperture a grating of strung iron is placed, so as to be in the centre of the furnace, and upon that grating the fuel is laid, and ignition is maintained by the air that issues into it through the eaves or vaults underneath.
The crucibles or pots are the most important article about a glasswork. The clay obtained at Stourbridge is found to answer the purpose better than any other. After carefully picking and brushing the clay, it is ground in a mill, and sifted through a sieve of about 20 passes in an inch : it is then wet with warm water, and well tramped in a large cistern, until it is brought to the consistence of a thick paste. Some manufacturers make up a very large quantity of this paste, and keep it in that state for many months : others, again, work it immediately into pots or crucibles. It is also common to take old crucibles and grind them down to a fine powder, which they add to the crude clay in quantities seldom exceeding a fourth part, from an idea that the burnt clay renders the crucible more refractory, and of course more likely to resist the com bined action of the fire and alkali required in the compo sition for glass. This mixture contracts less than if the pots were made entirely of crude clay, and of course is less liable to break while drying.