PHOTOGKAPHIC PKOCESSES 233 



Particularly during the operation of developing, and also, 

 if possible, during fixation, the plate should be frequently 

 rocked to ensure even action of the solutions, or one of the 

 mechanical rockers, already described, can conveniently be 

 used. 



To develop a quarter-plate, fully one ounce of developer 

 should be used. It is important to see that the plate is well 

 covered by the solution, otherwise air-bubbles may attach 

 themselves to the plate, and cause clear transparent spots to 

 appear in the negative. 



However safe the dark-room light may be, it is advisable 

 to cover the plate during development, and in all operations to 

 shield it as much as possible from light. For this purpose 

 it is convenient to have either a dish of a size larger than the 

 one in use to invert over the one containing the plate, or a 

 cardboard plate-box may be conveniently used to cover the 

 dish. 



When pyrogallic acid is used, it is as well to have fresh 

 developer for each plate. Eather rapid oxidation occurs with 

 this developer, and if it is used more than once, considerable 

 staining of the plate occurs. With the other developers this is 

 not the case, and they may be used two or three times, the only 

 effect being that they become gradually slower in action. 



In the case of a plate which is obviously not as it should be, 

 it is not always easy for a novice to judge whether it is over- 

 or under-exposed. In general, the over-exposed plates come up 

 very quickly when placed in the developer, and there is a lack 

 of contrast in the resulting negative. With under-exposure, 

 although there may be ample density in parts, there will usually 

 be some areas in which there is a total lack of detail. Further 

 than this, it is very difficult to indicate the differences between 

 under- and over-exposed plates, since the effect will vary so 

 largely with different objects. The over-exposed negative is 

 often thin, although it possesses ample detail in every part, 

 and in this case it ifcay be efficiently dealt with by the sub- 

 sequent operation of intensification. The under-exposed plate 

 can rarely be dealt with at all, and unless the negative is one 

 that cannot be repeated, it is far better to expose another plate 

 at once. 



The appearance of a number of small spots in the negative 



