21 



a convenient opportunity offers for bringing out the picture, which 

 is done in the most simple manner, with a material which can be 

 anywhere procured. 



It has been found by experiment, that the sulphate of iron has 

 the property of developing the latent images on papers prepared 

 with other salts of silver, and that by using the acetate bromide, 

 benzoate, etc., the most varied and beautiful effects are elicited. 



The calotype picture may, it is said, be developed in this way 

 after an exposure of one or two seconds only. 



CHRYSOTYPE. 



Sir John Herschel, whose various experiments have done so 

 much for the art of Photography, is the discoverer of this process, 

 and that of the Cyanotype, of which we shall next speak. They 

 are both founded upon the use of the salts of iron as photographic 

 \ agents. The Chrysotype process was communicated to the Royal 

 Society in June, 1843, and is as follows : 



Paper is washed over with a moderately concentrated solution 

 of ammonia-citrate of iron, and dried, the strength of the solution 

 being such as to dry into a good yellow colour, and not at all 

 brown. In this state it is ready to receive a photographic image, 

 which may be impressed on it either from nature in the caraera- 

 obscura, or from an engraving in a frame in sunshine. The image 

 so impressed, however, is faint, and sometimes hardly perceptible. 

 The moment it is removed from the camera, it must be washed 

 over with a neutral solution of gold, of such strength as to have 

 the colour of sherry-wine. Instantly the picture appears; not 

 indeed at once with its full intensity, but darkening rapidly up to 

 a certain point. At this point nothing can surpass the sharpness 

 and perfection of detail of the resulting photograph. The picture 

 is now to be rinsed in spring water, which must be three times 

 renewed. It is then blotted and dried, after which it is to be 

 washed on both sides with a somewhat weak solution of hydriodate 

 of potash. After being again rinsed and dried, it is now perfectly 

 fixed. If the nitrate of silver be used instead of the solution of 

 gold, the picture is brought out more slowly, and with much less 

 beauty. 



