CAMERAS AND PICTURE-MAKING 319 



stirring helps to prevent the formation of lumps that will require 

 a long time to dissolve. When the chemicals are completely 

 dissolved, pour the developer into the tray and put in a small 

 wad of absorbent cotton as large as a walnut. Be sure that 

 all light is excluded except that from the darkroom light. Take 

 the plate from its holder, handling it only by its edges. If oil 

 from the fingers makes a finger mark on the gelatine surface, 

 the developer will not get at the contained silver salts at this 

 point and your negative will show the finger mark. Immerse 

 the plate in cold water, then in the developer, which should have 

 a temperature of about 70 Fahrenheit. The film side of the plate 

 is to be kept up. Wipe off this side quickly but gently with the 

 absorbent cotton wet in the developer so as to remove any 

 adherent air bubbles. If this is not done the air bubbles may 

 prevent the developer from reaching the silver salts, and the 

 plate when developed will look as if dotted with pin pricks. 

 Rock the tray to keep the developer moving over the plate. 

 Lights and shadows should begin to appear in four or five seconds, 

 and the clear outlines of the object in ten seconds or so. If the 

 picture flashes up and the whole plate begins to darken at once 

 when it is put in the developer, it has been overexposed. If 

 the image comes very slowly and is weak, it has been under- 

 exposed. When the process of development is sufficiently 

 advanced so that the picture begins to show clearly on the back 

 of the plate, immerse it in water to wash off the developer and 

 put it in the fixer. This is a solution of sodium hyposulphite 

 together with other chemicals which tend to harden the gelatine 

 that has been more or less softened by immersion in the developer. 

 This "hypo" dissolves out of the gelatine film all the silver 

 compounds that were not reduced to metallic silver in the 

 process of development. The plate is left in the fixer until 

 all the yellowish white has disappeared ; this will take from three 

 to ten minutes. The plate is then washed in running water 

 for a half-hour to remove the fixer, and is stood on edge to 

 dry. Such a plate will display dark areas corresponding to 



