INTENSIFICATION 227 



on a negative. Photopake or some pigment in water or 

 gum- water is applied with a fine brush. 



Intensification. When a negative is too thin, or its 

 contrasts too weak, silver, mercury, or other body is 

 deposited on the image until the desired density is built 

 up as nearly as possible. A mercury and a chromium 

 formula, both very serviceable for this purpose, are given on 

 page 271. To ensure success it is necessary that all hypo 

 should be eliminated from the plate by thorough washing, 

 and that the plate be well washed between the bleaching 

 and blackening, and after the latter. A dried plate must 

 be immersed in water for half an hour before intensifica- 

 tion. 



If a negative is so thin that parts of it print too deeply 

 before details appear elsewhere, yellow water-colour may 

 be applied to the back of the negative on those parts, 

 and if judiciously done the details may print there almost 

 equally with the rest of the negative. 



Reduction. If negatives are too dense to print in 

 reasonable time, but contrasts are not too great, an 

 immersion in Howard Farmer's reducer will improve 

 them. This solution acts first on the shadows, that is 

 the faintly darkened parts in the negative, leaving the 

 high lights less acted upon. The result is that contrasts 

 are increased, but there is a danger of removal of faint 

 details. Great care must therefore be used in its applica- 

 tion. Only a dilute solution should be used, and a dish 

 of water kept at hand to plunge the negative into at any 

 moment to stop reduction. A careful application also 

 removes fog and brightens a negative. Ammonium 

 persulphate is another reducer with a different action ; 

 it attacks the high lights first, and consequently reduces 

 contrast. It is occasionally useful for over-developed 

 negatives. 



Printing Processes. The selection of a suitable print- 

 ing process has no small influence on ;he production of 



