PRINTING PROCESSES 449 



In another method, a positive print is gone over with waterproof India ink. In 

 this case the black hnes are covered. Judgment must be exercised as to the strokes 

 used, viz., crosshatching, curves, etc. With a little practice the results are unusual and 

 distinctive. Then the print is bleached so that the photographic image disappears 

 leaving only the hand-drawn sketch. 



A satisfactory bleach for disposing -of the silver image is 



Water 3>2 oz. 



Potassium permanganate 3 gr. 



Sulphuric acid 1 dram 



This will leave a discolored print. To remove the permanganate stain immerse 

 the print in a bath made up of 50 to 100 gr. of sodium bisulphite in 4 oz. of water. 

 This will leave a perfectly clean white print on which remain only the India ink lines. 

 Additional lines may be added to this print if desired. 



Since the India ink must be placed over the black lines of the original print, it is 

 sometimes difficult to tell when all the necessary lines have been covered, or to judge 

 how well the work has progressed. The solution to this difficulty is to place the 

 black fines on a negative print. In this case the ink is placed upon the white lines of 

 the negative.^ 



Lantern Slides. — Lantern slides are made on glass plates coated with an emulsion 

 somewhat similar to that used for making positives. Standard sizes are 3K by 4)4 in- 

 and 33<4 by S}i in. Several degrees of contrast are available. Eastman provides 

 soft, medium and contrast. The first two may be developed under a Wratten safe light 

 Series O or OA for contrast and medium plates; Series 1 safe light must be used for 

 soft plates which are more sensitive. 



Any negative that will make a good print will make a good slide. The slides may 

 be printed by projection or by contact. Blemishes must be kept to a minimum 

 because of their subsequent enlargement when the slides are projected. The Eastman 

 plates vary in sensitivity as follows: contrast plates require about three times the 

 exposure required for medium, and medium about seven times as much exposure 

 as soft. 



Exposure. — Using a 25-watt frosted lamp at a distance of about 6 ft. between light 

 and printing frame, the exposure required for an average negative on medium plates 

 is about 5 sec. It is advisable at first to make use of the test-strip method of deter- 

 mining correct exposure. Cover two-thirds of the slide with an opaque cardboard 

 and give an exposure of 40 sec; uncover part of the slide so that only one-third is now 

 covered, and give an exposure of 8 sec. Finally uncover the entire slide and give an 

 exposure of 2 sec. Now the slide will have portions exposed for 2, 10, and 50 sec. 

 In varying exposures, double or halve them, as smaller exposure changes will make so 

 little difference the operator will not learn much. To make positive from miniature 

 frames, use the positive stock film, print by contact; for 10 sec, 6 in. from a 10 cp. 

 lamp is a good trial exposure. Use weak developer. 



Development. — Slides may be developed in D-72 (see developers for paper, above). 

 Develop in a white tray and judge development as one would a printing paper. 

 When development is complete, the highest light should show appreciable 

 color. Dilute D-72 and develop as follows: soft plate, dilute 1 to 4, develop 2 to 3 

 min. at 70°F. ; medium plate, dilute 1 to 2, develop 1 to 2 min. at 70°F. ; contrast 

 plate, dilute 1 to 1, develop 3 to 5 min. at 70°F. 



1 There are several other modifications of the photo-sketching process. A good .survey of this 

 process will be found in Some Suggestions on Photo Sketching, by E. A. Yunker, Am. Phot., December, 

 1935, p. 740. 



