414 HANDBOOK OF PHOTOGRAPHY 



If the negative has been processed so that the brightness range of the original is cor- 

 rectly reproduced in opacity range, then a normal paper would be used. Prints 

 obtained in these three cases will all look alike, if the photographer has processed and 

 used his materials correctly. 



The photographer may make use of this ability to compensate for errors occurring 

 in the making of a negative or print. For example, the scientifically minded photog- 

 rapher knows the brightness range which may be expected from paper of certain 

 contrast. If he must photograph a scene in which the brightness range is greater than 

 this paper will reproduce, he will intentionally make a "soft" negative in which the 

 brightness range of the original has been compressed into the scale which can be repro- 

 duced by the paper. On the other hand if certain negatives are flat because of some 

 error in processing, the photographer may select a grade of paper which compensates 

 for this error. 



Printing Materials and Their Characteristics. Types of Silver Salt Materials. — 

 Printing papers are generally known as chloride, bromide, and chlorobromide papers, 

 these names indicating in a general way the chief ingredient in their emulsions. Chlo- 

 ride papers are the slowest and are used for contact printing; bromide papers, the 

 fastest of all printing papers, are roughly 100 times niore sensitive than the chloride 

 papers. They are used for projection printing. Intermediate in speed are the 

 chlorobromides; roughly one-twentieth as sensitive as the bromides. 



The chlorobromide papers are used when the operator wants the maximum control 

 over print color and contrast by variations of development procedure, and when the 

 simplest types of afterdevelopment toning are to be employed. 



Chlorobromides vary considerably in speed. Some are almost as slow as the 

 chlorides; others are almost as fast as the bromides; some may even be slower than 

 papers used for contact printing. These papers are usuallj^ not made in the wide 

 range of contrasts available in both chlorides and bromides, but a wide range of control 

 in warmth of tone is possible with them. Thej' have deeper blacks, and give a more 

 faithful rendering of shadows than chlorides or bromides. 



Characteristics of Printing Materials. — Curves representing the relation between 

 exposure and opacity (usually plotted as the logarithm of the exposure against the 

 density which is the logarithm of the opacity) of positive materials are similar to those 

 of negative materials. In general the straight or linear portions of these curves are 

 much shorter than those of negative materials. The effect of varying the processing 

 is markedly different for printing papeis than for negative materials, as illustrated 

 in the chapter on Photographic Materials. 



Printing papers are sensitive onl}^ to the shorter wavelengths, inz., blue, and can be 

 processed in yellow or red light. Negative materials, on the other hand, may be 

 sensitive to the entire visible spectrum and even beyond. 



Even to the light to which the paper is sensitive, printing papers are much less 

 sensitive than negative materials. 



Another difference between positive and negative materials lies in the manner in 

 which varj'ing contrast is secured. If the photographer prolongs the development of a 

 film or plate, the contrast increases. By variations in development procedure, con- 

 trast in negative materials may be controlled. But contrast is varied only to a small 

 extent by development variations when positive printing papers are processed. Con- 

 trast effects are obtained through proper choice of paper, rather than by methods of 

 processing. If a contrasty result is desired from a negative having normal gradation, a 

 contrast paper will be used. This contrast paper used with a soft negative will pro- 

 duce a normal print having normal gradation. Similarlj^ a soft print may be obtained 

 from a normal negative by the use of soft paper, and a normal result will be obtained 

 by using a soft paper with a contrasty negative. 



