416 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1951 



tions. The inside pages, bearing the illustrations, were printed litho- 

 graphically, and the remainder of the paper, bearing the bulk of the 

 text, was printed by letterpress. 



It is likely that difficulties in etching the minute dot structure of 

 relief plates made letterpress less feasible than lithography, at the 

 time, as a medium for use with the halftone screen. However, lithog- 

 raphers in general lost interest in obtaining halftone results during 

 the next two decades. There seemed to be little point in using screens, 

 which resulted in coarse halftones, when type could not be employed 

 at the same time. Screenless halftones in lithography could not com- 

 pare with the finer products of other processes, and so lithographers 

 concentrated mainly upon line work. After all, excellent halftones 

 were already obtainable through the photogravure and collotype 

 processes. The rapid development of collotype, which made use of 

 principles similar to lithography and which produced finer textures 

 and gradations, was probably an added factor in the decline of the 

 photolithographic halftone in the 1870's. Moreover, the Woodbury 

 process turned out screenless halftones that were distinguishable 

 from photographs only because they were richer in tonal value and 

 finer in detail. In any case the most pressing commercial need for 

 halftone was as a replacement for wood engraving — in other words, 

 in letterpress, where little or no progress had been made from Pretsch's 

 time to the 1880's. 



In 1866 Sir Joseph Wilson Swan patented his photomezzotint 

 process, which he claimed was adaptable to typographic (letter- 

 press), intaglio, and lithographic printing. Swan described a va- 

 riety of procedures, but most interesting for present purposes were 

 those in which he suggested the use of screens. One screen was made 

 by coating a sheet of glass Avith an opaque etching ground, ruling 

 through the ground to the surface of the glass, and using it as va 

 screen for producing halftone negatives. Another process involved 

 the use of particles of opaque matter either dusted on the negative 

 or incorporated in a solution of gelatin coated over the negative. Of 

 particular importance, however, was his suggestion for using a photo- 

 graphic negative perforated with minute holes. This negative, used 

 as a screen, would result in a diffusion of light, intense at the center 

 and shadowy at the periphery of the openings. This idea, the possi- 

 bilities of which Swan did not realize at the time, anticipated the 

 principle of modern halftone screens. This English scientist, who 

 was also of pioneer importance in developing the incandescent light, 

 made a further contribution to the diffusion of light in halftone screens 

 in his patent of 1879, which will be discussed later. 



Robert Faulkner, in 1872, made the first definite suggestion that a 

 screen out-of-focus be used to create a finer grain structure. Faulk- 



