ENAMEL is a substance of the nature of glass, but differs from it principally in two points ; first, in its be ing more easily fusible, which quality is given to it by the manner in which the flux is compounded ; secondly, in having a large proportion of either earth, or metallic oxide, united with the flux, to produce opacity. Some enamels are, however, very transparent, possessing great clearness and brilliancy of colour, in which case they differ from glass only in softness or easy fusibility. The best enamel that can be had for the purpose of making large plates for painting pictures upon, is the Venetian white opaque, with the name of Bertolini stamped upon the cakes, which cakes in general weigh about two pounds each. This article has not been imported for some years past, owing to the exclusion of the British Mader from the continent. The writer of this article has, however, been informed, that the maker of the best white enamel, whose name we have just mentioned, fell a sacrifice to French tyranny during their struggle for power in Italy and Naples. That this valuable article was the sole production of an individual, the manufac tore of which was unknown to any but himself, may lie inferred from the non-importation since the change of government in Italy, although every exertion has been used by those interested in the use of it, to obtain it at any price.
When enamel could be brought to England without restriction, it was generally sold for about six shillings per pound; but as it grew scarce, thirty shillings per pound was given, and, at the present time, it is as high as fifty shillings. This high price proved a great sti
mulus to those, who knew any thing about the nature of its ingredients, to exert themselves in their endea vours to ingredients, a substitute, and numerous were the tiialsof various persons to make an imitation. All attempts, however, were ineffectual, until very lately, when Mr Griffiths, of Round Court, Long Acre, London, suc ceeded in producing a hard enamel, superior to the best Venetian in whiteness, and much more valuable to the dial-plate makers. But the Venetian is still preferred for fluxed plates, used for portrait and historical paint ings; and, as these plates have always a coat of pure flux laid over the enamel, upon which the colours are laid, it requires a peculiar texture in the enamel, so that when the flux is melted upon it, a partial separation or cracking should not take place, which arises from the unequal expansion of the two substances. We have no doubt that the colouring material used with the flux to produce the white Venetian enamel, is the pure oxide of tin, commonly called putty. The manufacturers of putty in London, are in the habit of using SO per cent. of lead mixed with the tin, which assists the oxidation, causing it to proceed much faster than when the tin is used alone ; but the article made in this manner has a con siderable tinge of yellow, which renders it useless for the purpose of enamel, although it may suit the lapida ry or stone mason equally well as if it was made pure. (T. E.)