THE BOOK OF THE LANTERN. 163 



should be dried by heat, and there are many means of 

 doing this. An oven, not too hot, will do what is neces- 

 sary, but it is uncertain, for the heat may rise to such a 

 pitch that picture, gelatine, and all will curl off the glass. 

 A tin biscuit canister, divided into grooves, and placed 

 (dutch oven fashion) in front of a good clear fire is better ; 

 but the best plan that I have tried is the following : place 

 the glasses to be dried upon a flat iron plate above a gas 

 stove, the heat of which can be regulated. Upon the top 

 of the plate put a frame of wood, covered with fine muslin, 

 to keep off the dust. About twenty minutes of such treat- 

 ment will make the layer of paint on the glass so hard 

 that it can be worked upon with other colours, or sub- 

 mitted to the moonlight operation as already described. It 

 is during the operation of laying in the sky, &c., which may 

 be comprehended under the term " first painting," and the 

 subsequent drying, that access of dust must be carefully 

 guarded against. 



Lantern slides, by Whatever photographic process they 

 may have been produced, will stand a great deal of heat, 

 and they can be made hotter than the hand can con- 

 venie,ntly bear with impunity. This heat may be con- 

 tinued for about half an hour, and it will be found that 

 it has a kind of japanning effect upon the oil colours 

 employed ; indeed, the colours are by this means made so 

 hard that it is difficult, if not impossible, to remove them 

 afterwards without at the same time destroying the photo- 

 graphic image beneath the pigment. 



After the sky has been dried in the manner described, it 

 can easily be deepened, if found necessary, by the &pplica- 



M 2 



