Art of Painting in Enamel. 1-51 



with coke except in front An iron door, having an aperture in 

 it the size of the front of the muffle, closes the whole. The 

 entire draught of air supplying the furnace passes through the 

 muffle. The plates and paintings are placed on thin slabs, 

 made of tempered fireclay, technically termed planches. When 

 the fire has burnt up sufficiently, the plate or painting, after 

 having been dried by being placed on the iron plate opposite 

 the fire, is gradually introduced under the muffle, the planch 

 resting on the bed of coke. The greatest heat, it is obvious, 

 will exist at the back of the muffle; it is necessary therefore 

 that the picture should be turned while in the fire that it may 

 be heated equally over its entire surface ; this is effected by 

 means of a pair of spring tongs. When the colours are seen 

 to be properly melted the painting is wkhdrawn and placed 

 on the iron hearth to cool. In this furnace plates are prepared 

 and paintings fired from the smallest size up to about five 

 inches in diameter; but for larger works a furnace of a different 

 construction is required. The muffle of the large furnace has 

 a bottom and a back, and its mouth is closed also by a door 

 made either of iron or of fire-stone. From the circumstance 

 of its thus being closed on all sides it has acquired the ap- 

 propriate appellation of a close miiffle, that before described 

 being termed, in contradistinction, an open muffle; the essen- 

 tial difference being that while the entire draught of the fur- 

 nace passes through the latter, it is wholly excluded from the 

 former. In the large furnace the fire is placed under the 

 muffle only, and is supported by iron grate-bars, the construc- 

 tion, in fact, closely resembling that of a common air-furnace. 

 The draught passes between the bars and carries the flame 

 into the flue, which commencing at the top of one of the sides 

 of the fire-place, conducts it over the muffle, which it leaves^ 

 by means of flues constructed in the same plane with its bottom, 

 on the side opposite to that at which it enters. The flame after 

 enveloping the muffle plays against the bottom of an iron oven. 

 This oven contains several shelves, and its use is, to anneal the 

 paintings, this being necessary to prevent them from cracking 

 when in the fire, which they would do if exposed suddenly to 

 the heat of the muffle. The furnace is so arranged that the 

 bottom of the annealing oven becomes of a dull red heat at 

 the time when the muffle attains the proper state for receiving 

 the paintings, and this is indicated by its interior becoming 

 of a glowing orange heat, the muffle itself having to sustain a 

 heat nearly adequate to the fusion of cast-iron. By this ar- 

 rangement the paintings, as they are placed in the annealing 

 oven while it is cold, are gradually heated until they arrive at 

 a temperature at which they can with safety endure the much 



3M2 



