ENAMELLING. 421 



enamel is only about half the thickness on the concave as on the 

 convex side. For flat plates, the thickness is the same on both 

 sides. 



The plate, covered with the moist enamel powder, is warmed 

 and thoroughly dried, then gently set upon a thin earthen ring, 

 that supports it only by touching the outer rim, and put gradually 

 into the red hot muffle of the enameller's furnace. This furnace 

 is constructed somewhat like the assay furnace, but the upper part 

 alone of the muffle is much heated, and some peculiarities are ob- 

 served in the construction, to enable the artist to govern the fire 

 more accurately. 



The precise degree of fire to be given here as in all enamelling, 

 is that at which the particles of the enamel run together into an 

 uniform pasty consistence, and extend themselves evenly over the 

 surface, shewing a fine polished face, carefully avoiding on the 

 other hand so great a heat as would endanger the melting of the 

 thin metallic plate When the enamel is thus seen to sweat down, 

 as it were, to an uniform glossy glazing, the piece is gradually 

 withdrawn and cooled, otherwise it would fly by the action of the 

 cold air. 



A second coating of enamel is then laid on and fired as before, 

 but this time the finest powder of enamel is taken, or that which 

 remains suspended in the washings. It is then ready to receive the 

 figures and division marks, which are made of a black enamel, 

 ground in an agate mortar, with much labour, to a most impalpable 

 powder, worked up on a pallet with oil of lavender, or spike, and 

 laid on with an extremely fine hair brush. The plate is then stoved 

 to evaporate the essential oil, and the figure burnt in as before. 

 The polishing with tripoli, and minuter parts of the process, need 

 not be here mentioned. 



If the enamel be chipped off a dial plate (which may be done 

 with the utmost ease, by bending it backwards and forwards, as 

 the adhesion between the metal and glazing is very slight) the part 

 immediately ia contact with the copper will be found deeply and 

 nearly -uniformly browned, which shews how unfit copper alone 

 would be for the transparent enamels. 



The* regulation of the fire appears to be the most difficult of all 

 the parts of this nice process, particularly in the fine enamelling 

 of gold for ornamental purposes, of designs, miniatures, and the 

 like, where three, four, or sometimes five separate firings are re. 



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