2336 Journal of Applied Microscopy 



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LABORATORY PHOTOGRAPHY. 



L. B. ELLIOTT. 

 Devoted to Methods and Apparatus for Converting an Object into an Illustration. 



In many of the processes of developments in the laboratory stained nega- 

 tives are likely to result and, as they are usually considered a hopeless blemish 

 to the negative, we believe the following paper on the " Removal of Developer 

 Stains," by R. E. Blake-Smith, contains many practical suggestions for the 

 removal of stains from negatives, and which we take in part from " Photography," 

 will be of practical value to our readers : 



" In most text-books of photography ' clearing solutions ' are described which 

 many of the writers affirm remove the yellow or brown stains caused by a care- 

 lessly used developer. These solutions are merely acid solutions containing a 

 hardening agent like alum, which prevents the acid frilling the film. The best 

 of these solutions is probably a three per cent, solution of hydrochloric acid, 

 which is applied to the plate after it has been soaked in the formalin bath. 



" These solutions may be safely relied upon in the majority of cases to lighten 

 the stain, but they will never remove it altogether. 



" If one needs a more radical cure, as will be necessary in the case of uneven 

 stains, one must adopt much the same process as is applied in ' bleaching ' 

 fabrics. The two chief bleaching agents of commerce are bleaching powder and 

 sulphurous acid. The former, which is by far the most important, is manu- 

 factured by passing chlorine over slaked lime. Bleaching powder is used in 

 acid solution, and bleaching by oxidation, owing to the action of chlorine and 

 hypochlorous acid. Sulphurous acid bleaches by reduction, and its use is limited. 



" My present object is to bring before photographers the use of these two 

 substances as applied to the removal of developer stains. First, however, it 

 must be said that the nature of such stains on a negative varies very much with 

 the composition of the developer and with the way in which the stains them- 

 selves have been formed. 



" One thing is certain ; it is always better and quite easy to take precautions 

 against getting any developer stains on one's negatives. Plenty of a soluble 

 sulphite should be used in the developer itself, and after development the plate 

 should be washed at first in a solution of sodium sulphite, or directly fixed in 

 the bisulphite hypo bath — the ' acid ' bath. When the time comes for drying 

 the negative it should be put up to dry in some place where there is no chance 

 of it being splashed with injurious solutions. Still, owing to an occasional 

 lapse into careless ways, one may get every now and then an unevenly stained 

 negative. 



" Then, the first process which should be gone through is to harden the film 

 of the negative in the formalin hardening bath. It can after that be treated with 

 Sodium sulphite, ..... 35 grains. 



Sulphuric acid (concentrated), . . 12 minims. 



Water, ....... 1 ounce. 



