TONING. 



373 



388) is usually preferable on account of the shorter time of ex- 

 posure requisite. 



Expt. 395. Toning Silver Prints. Particles of silver reduced 

 from silver compounds by the action of light possess the property 

 of attracting other silver particles to them from a mixture of solu- 

 tions which would spontaneously cause the deposition of metallic 

 silver in virtue of chemical changes set up between the dissolved 

 substances ; and this property is utilised in intensifying negatives, 

 &c. (Expt. 391). In somewhat similar fashion, a paper silver print, 



Fig. 202. Fern Leaf (Positive). 



Fig. 203. Fern Leaf (Negative). 



when placed in contact with certain fluids containing gold, platinum, 

 and various other metals, possesses the property of attracting par- 

 ticles of gold, &c., to those parts where the silver deposit is thicker, 

 to a greater extent than to those portions of the surface where it is 

 thinner; so that gold, &c., is withdrawn from the fluid and 

 deposited on the print, modifying the colour of the silver particles 

 contained therein. Accordingly, silver prints are frequently 

 " toned " before finally fixing them by immersing them in a " ton- 

 ing bath " consisting of a weak solution of chloride of gold mixed 



