Toning

Toning. The photographic prints obtained upon the ordinary silver paper of photographers have neither a permanent nor pleasing colour, and have therefore, before fixing, to be subjected to a process known as toning. This is usually effected by immersing the prints for some time in a bath containing a solution of chloride of gold and other salts, e.g. sodium acetate or borax, The colour of the print is seen to alter and pass through a series of colour from brown to a deep purple, the paper being taken out when the desired tone is obtained. The exact tone obtainable, however, varies with the paper and the composition of the toning-bath, and a considerable amount of experience is required to obtain the best results. The prints are afterwards washed and fixed by immersing in a solution of sodium thiosulphate. The exact chemistry of the process is still a matter of some uncertainty. It is usually regarded as dependent on a substitution of of gold for the silver of the image. Many other solutions, however, may be used for toning, as solutions of platinum, ammonium sulphide, iron, etc., and it may be due, in some cases, to an alteration of the molecular state of the silver deposit,