ADDITIONAL FIXING BATHS.
It is always a good plan to have two baths ready : so that when all the prints have been passed into No. 1 bath, those that were placed there first may be trans ferred to No. 2. This ensures proper fixa tion, and prevents overcrowding. In the ease of the combined bath, it is also a from this stock solution, and may be used as it is for plates, or diluted with an equal bulk of water for prints. Fig. 346 shows a good form of appliance. Some workers prefer to use a contrivance something like a colander, in which the crystals are placed, and the hot water poured over, as in Fig. 347. An arrangement for upward filtration, as described in the section on " Printing-out Processes and Papers " (p. 168), may be used : substituting, of course, a piece of canvas or netting for the muslin. The crystals, if preferred, may be sus pended in a muslin bag. Do not make up the hypo. bath just before toning ; in fact,
it is better not to touch it at all if it can be avoided.
good plan to have an additional fixing bath, since it is seldom that the prints can he sure of proper fixation in the same time as that taken for toning. In the case of toning, the time of immersion may he varied according to the colour desired ; but in fixing it must always continue until the effect is complete. If the solution is too weak, a salt of silver-hyposu]phite is formed, insoluble in water. This is pro bably the most fruitful cause of fading and deterioration. A fresh bath should, there fore, be used for each batch of prints. Hypo. is extremely cheap, and it is poor economy to use old baths which are weakened by use and contain silver. If the bath has been used even once before there is always great danger of stained lights.