160 Laboratory Arts 



Without the addition of citrate of soda a very ordinary negative 

 will result, and will usually require intensification. With citrate 

 of soda, development may be pushed until the picture completely 

 disappears until the plate becomes completely black. Then it is 

 removed from the developer, rinsed quickly in a basin of water, 

 and immersed at once in a dish containing a fixing solution, which 

 consists of 2 Ibs. hyposulphite of soda and 2 oz. metabisulphite 

 of soda, and a Winchester quart of water. The plate is kept 

 immersed until the back of the plate looks perfectly black, and on 

 being held up to the light, the whole plate is clear and transparent. 

 It is then removed to a rack, washed for half an hour in running 

 water, drained and dried. All these operations are conducted 

 with the plate film upwards, and only the edges of the plate may 

 be touched with the fingers. Special care must be taken to keep 

 the hands, bench, dishes, camera, and all appliances absolutely 

 clean and free from the hyposulphite solution, otherwise endless 

 trouble and disappointment will result. In removing the plate 

 from " fixing bath," care must be taken not to allow even a single 

 drop to fall upon bench, floor, or anywhere where it may pass 

 unnoticed until crystallization indicates its whereabouts. Should 

 this occur, the solid may be crushed, and sent into the air as a fine 

 dust, settling upon the unexposed plates, which then commence to 

 " fix" the instant they are placed in the developing solution. Pin- 

 holes will result, and are frequently due to this cause alone. Hence 

 frequent swilling of all dark room appliances, and the use of plenty 

 of washing water are to be strongly recommended. 



All solutions used should be at about the same temperature, con- 

 sequently it is recommended that they be kept in the dark room, 

 where the whole of the above operations are to be conducted. 



The plates referred to above are capable of withstanding very 

 rough treatment. After washing for ten minutes, for example, 

 they may be drained a few moments, dried by wiping with a wet 

 chamois leather, and subsequent standing before a fire. Any 

 ordinary film so treated would melt off the glass. 



Over exposure or under exposure are the principal causes of 

 failure to secure satisfactory negatives, the other possibilities of 

 straying being largely corrected by the use of the plates recom- 

 mended, and by exposing in the manner suggested. Over 

 exposure is detected by the rapidity with which the picture appears. 

 An over-exposed plate shows up its picture rapidly under 

 development, but before it has time to gather density or definition, 

 the plate blackens, and one has to transfer it to the fixing bath. 

 The plate so produced is "thin" and the definition is poor, 



