GLASS FOR HOUSEHOLD USE AND FAXCY PURPOSES. 123 



Captation of the antique and other styles of ornamentation to articles 

 of daily use, and some fine specimens of high art on tazzas, &c, are 

 also shown. The foreign department contains some very fine specimens, 

 particularly of figure engraving. It must be admitted, that to foreign 

 workmen this country is much indebted for manipulation in this ex- 

 ceedingly delicate and pleasing art, which promises to take an equal 

 place if not to excel that of the glass-cutter. Certain it is, that the 

 manufacturer, by the taste and style of the modern engraved ornamen- 

 tation, is driven to the use of finer and more classical shapes. 



Under the head of flint glass, the Jurors would notice the improve- 

 ments in it for optical purposes, made by Messrs. Chance, Brothers, aud 

 Co., a member of which firm was one of the Jurors, and Mons. Bon- 

 temps, one of the experts of this class. These gentlemen, as far back 

 as the Exhibition of 1851, had made great progress, having patented 

 twenty-five years since the process first discovered by Mons. Guinand,* 

 in Switzerland. It had long been suspected that the want of homo- 

 geneity in flint glass, whereby it was rendered of but comparatively 

 little use for optical purposes, was not due to any want of chemical 

 mixture of the materials, but solely to the precipitation by gravitation 

 of the heavier ingredients of the mixture. This had been successfully 

 proved by Professor Faraday. Many years since, Sir Humphry Davy 

 sought to remedy this, endeavouring, by long continued and excessive 

 heat, to boil the mixture, so to speak, and thus to overcome the want 

 of homogeneity. 



This, as might be conjectured, failed, and for a very good reason ; 

 it being almost impossible to subject the whole body of the materials 

 to the same degree of heat at the same time ; by a natural law, the 

 portions subjected to the greater heat are constantly replaced by those 

 in a lower state of caloric ; this constant interchange of particles pro- 

 ducing striee. They also absorbed the alumina of the pot, and the glass 

 became of a gelatinous app.arance. To obviate this defect, Messrs 

 Chance and Bontemps followed out the experiments of Guinand, and 

 Professor Faraday, and by constant mechanical agitation during the 

 fusion of the materials, overcame the gravitation of the heavier matters, 

 and thereby a much greater homogeneity of the mass was obtained. 

 This discovery has led to a much greater certainty in the manufacture 

 of flint glass for optical purposes, which previously was a matter of 

 , ccident. 



In plate glass, the Jurors remark, with satisfaction, the superior 

 piality which both the British and foreign departments continue to 

 Toduce. This is a manufacture almost perfected. That there has been 

 no retrogression is certain, although advance now becomes very difficult. 

 In the attempt to improve the colour of plate glass, the Jurors would 

 warn manufacturers against the use of manganese, or other materials to 



* 'Some account of the late Mr. Guinand, of Brenets, Neufchatel, Switzer- 

 land." by S. P. de B.— Longman and Co., 1825. 



