450 HANDBOOK OF PHOTOGRAPHY 



The plates should be rinsed in a short-stop bath and then fixed in any good harden- 

 ing fixing hath. They should be washed 20 min. 



Mounting. — The slides should be varnished to protect them and prevent absorp- 

 tion of moisture in damp weather, which causes "dewing" or condensation of moisture 

 on the cover glass when it is heated by the lantern. Special varnish for this purpose 

 may be purchased from the supply houses. 



The shape of the mask should usually be rectangular. Oval or round masks are 

 seldom necessary or desirable. The standard size mask opening for motion-picture 

 theaters is 3 by 2^^ in. The mask, which may be cut from black paper or purchased 

 ready to use, is placed on the emulsion side of the slide. 



After masking, the slide is bound in contact with a thin cover glass which is placed 

 on the emulsion side. A white spot or label should be placed on the lower left-hand 

 corner when holding the slide in the hand so that the image appears on the screen 

 properly. This label not only identifies the slide but is useful to the projection- 

 machine operator in inserting the slide in the machine properly. 



Cover glasses for slides 2 in. square are now available for Kodachrome and other 

 positives made with cameras using 35-mm. film. These slides are mounted and bound 

 in the same manner as the larger slides. Cellulose or Scotch tape may be used to bind 

 up the positive with its cover glass. 



Direct Positive Paper. — This paper is used for making negatives which, by the 

 reversal process, are changed into positive prints. Correct exposure for the negative 

 determines the quality of the print, therefore a fixed light source and a definite 

 exposure are required. Underexposure will produce a dark picture, while overexposure 

 produces pictures which are too light. 



The reversal process includes exposure, development of the negative, bleaching the 

 negative, clearing, reexposure, development of the positive, fixing. Fixing is not 

 essential, but it gives the print a slightly increased brilliance. Fixed prints should be 

 washed for 10 min. in running water. If not fixed, prints should be washed for 4 or 

 5 min. The Eastman direct positive emulsion is coated on a waterproof support 

 which permits rapid drjdng. An inexpensive electric hair dryer can be used effectively 

 to facilitate drying. The Series 2 Wratten safe light should be used for workroom 

 illumination. 



A satisfactory division of time in the different solutions is as follows: developing, 

 45 sec. to 1 min.; bleaching, 30 sec; clearing, 30 sec; developing or redeveloping, 

 30 sec; fixing, 30 sec. It is necessary to wash the prints thoroughly in iiinning water 

 for at least 15 sec. between the different solutions. When the solution D-88 is used for 

 developing a black-and-white positive, it is necessarj' to expose the paper to artificial 

 light directly after clearing. If convenient, the white light may be turned on as soon 

 as the prints are placed in the clearing bath. 



Developer (D-88) 



Water (about 125° F.) (52° C.) 96 oz. 3 1. 



Sodium sulphite (desiccated) 63-2 oz. 195 g. 



Hydroquinone 3 J'i oz. 97 . 5 g. 



Boric acid (crystals) l-i oz. 22 . 5 g. 



Potassium bromide 150 gr. 10 . 5 g. 



Sodium hydroxide (caustic soda) SV^ oz. 97.5 g. 



Water to make 1 gal. 4 1. 



The caustic soda should be dissolved in a small A'olume of water, in a separate 

 container, and added to the solution which has been made bj^ dissolving the chemicals 

 in the order given. Water should then be added to make 1 gal. (4 1.). When dis- 

 sohdng the caustic soda, stir constantlj' so that the heat generated will not cause the 

 solution to boil with explosive violence and spatter the hot caustic on the hand and 



