E N A 



I :>' i- the process for firing and finishing the glass 

 enamel plate*. We shall now describe the method 

 adopted to tire nnd finish the hard enamel dial*. 



The firing of these when the enamel is laid on, is the 

 ante a* for the glass enamel, the apparatus being used 

 for both purposes ; but the heat applied to melt the 

 Venetian hard enamel must not be so great, and the 

 plate must be taken from the fire as soon as the enamel 

 la found to form one tolerably compact body, as any 

 longer continuance would have n tendency to spoil the 

 intended shape of the plate, which is always considered 

 a mot essential quality in hard enamel plates. The 

 method of using o/Tthe hard enamel plates is different 

 from that made use of in the glass enamel ; for as the 

 proportion of flux in the Venetian hard enamel is con- 

 siderably less than in the glass, and as diminishing the 

 flux by using it off, (if carried to the extent we have 

 before described,) would render the surface very po- 

 rous, great care is necessary to be observed that the 

 flux may be raised to the surface in the first fire as little 

 as possible ; which is done by giving the plate a very 

 alight heat, barely sufficient to unite the particles of 

 enamel into one solid mass. Should any specks ap- 

 pear, they must be taken out with the graver, as 

 was directed in the glass enamelling, and the surface 

 must be reduced to perfect evenness, by rubbing it with 

 a grey stone, or what is still better, the water of air 

 >tnne found in Scotland, and now much used by mathe- 

 matical instrument makers. This method of using off' 

 must be continued until the surface is smooth, and all 

 the old or first gloss is removed. This part of the pro- 

 cess should be very carefully performed, for should the 

 plate receive any strain, it would be cracked in the fire, 

 and inevitably spoiled, to prevent which, it will be best 

 to hold the plate in the fingers of the left hand while 

 the stone is rubbed lightly over every part of its sur- 

 face. The plate must then be well washed with very 

 clean water ; and to prevent any particles of the stone 

 remaining in the pores, it is customary to rub the sur- 

 face for about five minutes with a piece of soft smooth 

 hoop wood, or what is still better, if it can be had, 

 toft dog wood cut quite flat and smooth. When this 

 i- done, the plate must be well washed and wiped, and 

 will then be ready for the fire. 



The heat for finishing may be rather more than that 

 used in the first fire, as in tliat instance the intention 

 was only to unite the particles of enamel into one solid 

 mass. But the principal object in finishing being to 

 raise the flux to the surface as much as possible, a 

 greater heat may be used with advantage ; but the plate 

 must be taken from the furnace the instant tluit the 

 surface appears bright and glossy. 



We shall conclude our directions for firing the plates, 

 with some general observations upon the accidents that 

 .ire most likely to occur in both kinds of enamelling, 

 and point out the best methods to remedy them when 

 they happen. Where good Venetian enamel cannot be 

 obtained, and mixtures of various kinds are resorted to, 

 it frequently happens that the glass enamel plates crack 

 when they are brought to the second fire. This is no 

 doubt owing to the unequal expansion of the two ena- 

 mels; and where the cracking takes place at the top or 

 upper side of a plate, it requires very delicate treat- 

 ment to preserve the dial from being completely spoil- 

 ed 



K N G 



To <lo this successfully, as soon as the crack is ob- 



!, the plate must be withdrawn from the fire ; and 

 if it extend- only from the centre hole to the edge, it 

 will, in most cases, bear mending, but if it has taken 

 place in two or three places, it will In- useless to make 

 the attempt, as it will rarely succeed. If the dial plate 

 was to continue in the fire, after it is cracked, a suffi- 

 cient time, the enamel would close, and the plate become 

 sound again. But as the copper on its surface is in a 

 state of oxidation, the oxide of copper, uniting with 

 the enamel, would rise to the upper nil-face of the 

 plate, producing by its union a faint and sometimes a 

 dark green line, which would evidently render the 

 plate useless. The operator, therefore, must observe the 

 time when the crack has opened to its greatest width ; 

 and before it unite or close at the bottom, the plate- 

 must be withdrawn from the furnace and allowed to 

 cool. The opening must then be filled with fine ena- 

 mel, laid sufficiently high to allow for its running down 

 in the fire ; but to adjust the quantity, so as to prevent 

 the appearance of a seam across the plate, will require 

 much judgment ; and, indeed, however well the ope- 

 ration may succeed, it will still remain visible, be- 

 cause the mending cannot be submitted to the process of 

 using off", as the plate would, by Mich means, be ren- 

 dered in parts very porous, and thereby contract dirt 

 when the fingers touch its surface. 



Another very common accident in making glass ena- 

 mel plates, is to ovcrjire them, (as it is technically call- 

 ed. ) Whenever this happens, the arsenic, which give* 

 opacity and whiteness to the material, is converted into 

 a flux by the extreme heat, nnd that part of the plate 

 which has been so treated becomes serai -transparent 

 and of a light blue colour. The only method that can 

 be used in that case, is, to return the jplate into tho fire, 

 and give it a longer continuance of heat, but as slight 

 as possible, just keeping it red hot ; and to do this con- 

 veniently, the turner should be brought nearer to the 

 front of the muffle, as the greatest heat is always at the 

 back. This treatment will restore the plate to a tolerable 

 degree of whiteness, by reviving the powers of the 

 arsenic ; but it must never be expected to look as white 

 as if it had been properly fired. Should any crack ap- 

 pear on a hard plate, it would be in vain to try to mend 

 it; for as the shape of the dial in hard enamelling may 

 be brought to such great perfection, when all parts of 

 the process succeed, it is almost needless to say that 

 the plate would suffer so very much in this point as to 

 make it good for nothing. An accident, therefore, of this 

 kind may always, in hard enamelling, be considered as 

 the close of an abortive attempt. ( T. E. ) 



ENARGEA, a genus of plants of the class Hexan- 

 dria, and order Monogynia. See BOTANY, p. 189. 



ENCAUSTIC PAINTING. See PAINTING. 



ENCELIA. See Pallasia, BOTANY, p. 308. 



ENCHYLjENA, a genus of plants of the class Pen- 

 tandria, and order Monogynia. See BOTANY, p. 171. ; 

 and R. Brown's Prodromut, &c. p. 407. 



ENDEAVOUR RIVER. See NEW HOLLAND. 



ENDECANDRIA. See BOTANY, p. 267. 



ENDIANDRA, a genus of plants of the class Trian- 

 dria, and order Monogynia. See BOTANY, p. 112 ; and 

 R, Brown's Prodromus, &c. p. 402. 



ENFIELD. Sec MIDDLESEX. 



ENGINE DIVIDING. See GRADUATION, 



