568 HANDBOOK OF PHOTOGRAPHY 



at the proper temperature, it will remain so for a reasonable period. Rubber or 

 bakelite tanks will break; metal tanks will dent if dropped on a hard surface. 



Certain small metal tanks for plates or films have tight-fitting covers, rubber 

 gasketed, so that the tank may be inverted during development insuring that the 

 solution is properly agitated. They may be fitted with spigots and filling spouts so 

 that only the loading need be done in the darkroom. 



Large tanks for photofinishing and motion-picture processing are best purchased 

 from manufacturers specializing in this type of equipment. They may be made of 

 wood, steel covered with thin soft rubber, earthenware, etc. 



Tray Cleaners. — Trays frequently become discolored from silver and dye or from 

 the oxidation products of developers. Two formulas for tray cleaners are given below. 



Tray Cleankr (Eastman TC-1) 



Water 32 oz. 11. 



Potassium bichromate 3 oz. 90 g. 



Sulphuric acid (pure concentrated) 3 fl. oz. 96 cc. 



Silver-stain Remover (Eastman TC-2) 



Water 32 oz. 11. 



Potassium permanganate 73 gr. 5 g. 



Sulphuric acid (pure concentrated) 2^^ drams 10 cc. 



Add the acid slowly to the solution while stirring the solution rapidly. 

 Pour the solution into tray and swish around so that all tray parts are covered. 

 Then rinse and use the following: 



Clearing Solution 



Water 32 oz. 11. 



Sodium bisulphite 145 gr. 10 g. 



Wash trays well after applying the clearing solution. Acid dyes as used in imbibi- 

 tion color printing may be removed from trays by the use of ammonia. 



Sinks. — The sink is a most important part of the darkroom equipment. It should 

 be centrally located so that no unnecessary steps must be taken to get to it from any 

 part of the darkroom. It must be large enough to accommodate the largest trays in 

 the laboratory. It should be so constructed that a portion of it may be blocked off 

 with a weir which divides the sink into two portions, one containing the drain and the 

 other either without a drain or fixed with a good stopper. In this manner, water at the 

 proper temperature maj^ be used in one portion while access to the drain is available 

 in the other portion. 



Sink materials may be wood, properly treated, stoneware, lead-lined wood, or 

 porcelain. Wooden sinks are not expensive to make. Cypress or maple may be 

 used. Individual pieces of the wood should be tongued and grooved and then held 

 together with strong bolts or braces. The inner surfaces which come into contact 

 with liquids should be given several coats of a corrosion-resistant paint before being 

 used. Each coat must be allowed to dry thoroughly before the next is applied. If the 

 paint is light in color, it will probably stain, but will reflect light from the overhead 

 illumination and contribute to the general illumination. 



A rack should be arranged to be moved about over the top of the sink so that trays 

 may be placed upon it with the certainty that liquid slopping out will fall into the sink 

 and be disposed of through the drain. Shelves back of the sink should be deep enough 

 so that bottles cannot fall off into the sink or into trays of solution. 



Another useful adjunct to the sink is a float in which trays may be placed and 

 supported in a water bath of a required temperature. Such a float may be made of 

 wood in which a rectangular space has been cut of such a size that the overhang on 

 the tray top will prevent the tray from falling through into the sink. If, then, one 



