1 62 Laboratory Arts 



a white ground appear. This is, however, not strictly the case, 

 the black ground is certainly covered with a grey deposit, but the 

 original white lines owe their apparent blackness now to their 

 transparency, in contrast with the ground. 



The plate is now to be thoroughly washed, and the subsequent 

 failure or success of the negative largely depends upon the thorough- 

 ness of this washing. At least an hour in running water should be 

 given, and as much longer as is convenient. When thoroughly 

 washed, the plate is removed to a bath of dilute ammonium 

 hydroxide solution (the strength does not matter much) where it 

 blackens ; the completeness of the operation being judged by the 

 appearance of the back of the plate, which should be perfectly 

 black. After two or three minutes in this solution the plate is 

 lifted out, washed, drained and dried as before. The film must 

 not now be dried before a fire or by any such method ; it must be 

 dried slowly and perfectly drained. 



Rapidity in drying may be secured in all cases of plates, by 

 soaking the plate for ten minutes in methylated spirit, and drying 

 by exposure to air, after wiping with chamois leather. The process 

 is not to be recommended, as in drying some transparency is 

 frequently lost. Rectified spirits of wine does not produce this 

 loss of transparency to quite so great an extent, but it is expensive. 

 The best way of all is to drain and air dry. 



Intensification should not be looked upon as a necessity ; good 

 negatives, and perfectly satisfactory black and white copies, can 

 easily be obtained without this process ; it must be regarded merely 

 as a way of improving a poor plate. It is a question whether the 

 process is really worth while, but inasmuch as it enables a poor 

 plate to produce a good print, it is included here. 



The actual lantern slide, termed a " positive " or " transparency," 

 is now to be made. The dry plate is placed, film inwards, in a 

 J-plate printing frame, and a lantern plate placed above it, the two 

 films being in contact. The best plate on the market is " Thomas' 

 Lantern Plate," which even the Germans use. This plate is very 

 thin, the film sensitive and capable of producing dead black lines 

 upon an absolutely transparent ground ; not a single lantern plate 

 of this make need ever be wasted. Having placed the positive in 

 position, make sure the required print is in the centre of the plate, 

 and fasten up the frame. Expose by holding up to a gas flame, 

 2 feet from a No. 3 Bray gas burner, for 12 seconds will usually 

 suffice. With a thin negative take 1 5 seconds 3 feet away, and 

 with a very strong negative 12 seconds at a foot. 



Development and fixing are proceeded with as before, but no 



