424 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1951 



The halftone plate now used in letterpress printing begins with 

 a screen placed in the camera at a proper distance from the sensi- 

 tized film. The image is photographed through the screen, the light 

 passing through the clear squares so that the original image is broken 

 up into minute dots of varying sizes depending upon the fineness of 

 the screen and the amount of light reflected from the copy. The film 

 negative is then stripped from its celluloid or glass base, placed upon a 

 piece of clear glass, and exposed to strong light over a copper plate 

 coated with a solution of bichromated gelatin. Light hardens the 

 portion of the plate which will eventually become the raised or print- 

 ing surface. The unhardened gelatin is washed off, exposing the bare 

 copper for etching. The plate is then etched in several stages with 

 perchloride of iron, the sides of the dots being dusted with an acid 

 resist, dragon's blood, at each stage. The dots in relief, when inked 

 and printed, recreate the original. This brief summary merely touches 

 upon some of the most important operations in platemaking and gives 

 no indication of the skill and care required. 



Many important developments, particularly in recent times, have 

 been omitted because of the necessity for condensation. Nevertheless, 

 we have touched upon the high points in the growth of the halftone 

 process, and noted how the development of a reliable screen was the 

 main factor in finally removing the barriers to cheap, rapid, and faith- 

 ful reproduction of continuous-tone pictures. The achievements were 

 not confined to letterpress, as we have seen, but were carried over into 

 lithography and gravure as well. It was letterpress, however, the 

 last major process to obtain photomechanical halftones, that began 

 the era of modern high-speed printing of halftone subjects. 



From this beginning sprang great industries, trades, more rapid 

 means of communication, clearer and more efficient means of education, 

 and other technical advances that have done so much to give our civili- 

 zation its distinctive character. Our modern conception of advertis- 

 ing, for example, with its stimulus to business, leans very heavily upon 

 the use of the halftone screen. The present wide use of color printing, 

 with its added attractiveness and veracity, would not have been pos- 

 sible without the perfection of the halftone screen. It has made 

 possible the popular and widely circulated picture magazines through 

 which much entertainment and educational matter is given mass cir- 

 culation. It serves as an indispensable tool in recording scenes and 

 events for immediate use in newspapers and in news periodicals. It is 

 indispensable in preparing such printed advertising as mail-order 

 catalogs, which serve the public as pictorial department stores. Tech- 

 nical books, art books, children's books, posters, calendars, greeting 

 cards, house organs, fiction and home magazines — these and publica- 

 tions of a hundred other kinds all derive a great part of their beauty 

 and effectiveness from the use of halftones. 



