ENAMELLING. 4 .! < 



-cess. The above proportions, however, are not invariable, for if 

 more fusibility is wanted, the dose of oxyd is increased, and that 

 of the sand diminished, the quantity of common salt remaining the 

 same. The sand employed in this process, according to Mr. Clouet, 

 is not the common sort, however fine, but a micaceous sand, in 

 which the mica forms about one-fourth of the mixture. 



Neri, in his valuable treatise on glass-making, has given long 

 ago the following proportions for the common material of all the " 

 opaque enamels, which Kunckel and other practical chemists have 

 confirmed. Calcine 30 parts of lead, with 33 of tin, with the 

 precautions mentioned above. Take of this calcined mixed oxyd 

 50 pounds, and as much of powdered flints (prepared by being 

 thrown into water when red hot, and then ground to powder), and 

 ight ounces of salt of tartar; melt the mixture in a strong fire 

 kept up for ten hours, after which reduce the mass to powder. 

 This is the common material for the opaque enamels, and is of a 

 grey white. To make this fine enamel quite white, mix six pounds 

 of this material with 48 grains of the best black oxyd of manga- 

 nese, and melt in a clear fire. When fully fused, throw it into 

 cold water, then re.melt and cool as before two or three times, till 

 the enamel is quite white and fine. Kunckel observes on this pro- 

 cess, that he tried it without the oxyd of manganese, but the ena- 

 mel, instead of being milk white, was blueish and not good, so 

 that there is no doubt but that this oxyd is highly important. If 

 too much is used, the enamel becomes of a rose purple. For fur. 

 ther observations on this subject, see the article Glass. Colour, 

 ed enamels are composed of a common basis, which is a fusible 

 mixture of verifiable materials, and of some metallic oxyd. In 

 general, the coloured enamels are required to be transparent, 

 in which case, the basis is a kind of glass, composed of borax, 

 sand, and oxyd of lead, or other vitresccnt mixtures, in which 

 the proportion of saline or metallic 11 ux is more or less accord, 

 ing to the degree of heat that the colouring oxyd will bear with, 

 out decomposition. When the coloured enamel is to be opaque, 

 or opalescent, a certain portion of the white opaque enamel, 

 or of the oxyd of tin, is added to the mixture. The most beau, 

 tiful and costly colour known in enamelling, is an exquisitely line 

 rich red, with a purplish tinge, given by the salts and oxyds 

 of gold, especially the purple precipitate, formed by tin in ons 



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