HALFTONE SCREEN — KAINEN 413 



Halftones in litliograpliy were obtained as early as 1852, shortly 

 after the appearance of Talbot's patent. Leniercier, a Parisian lithog- 

 rapher, working Avith Barreswil, Davanne, and Lerebours, sensi- 

 tized a lithograph stone with asphaltum, exposed it under a negative, 

 and washed the stone with ether, which removed the unhardened areas 

 of asphaltum. The stone was then inked and printed in the usual 

 manner, the grain of the stone providing an ink-holding surface. 

 Some excellent results were obtained, but the costliness of the process, 

 together with the low light-sensitivity of asphaltum and the corre- 

 spondingly long exposures required, made the process impractical. 



Poitevin's 1855 patent, which described the use of bichromated 

 solutions of gum, gelatin, and albumen (white of egg) , marked a great 

 improvement in photolithography. The sensitized stone was exposed 

 under a negative, the image was developed under water, with the 

 undeveloped areas washed awa}^, and the stone was inked and printed. 

 J. S. Petit, in his "Modern Reproductive Graphic Processes," 1884, 

 described substantially the same process, with the exception that the 

 stone was inked prior to washing, as the process most in use in photo- 

 lithography a't the time. As a matter of fact, the albumen process 

 was universally used even after halftone screens were adopted in 

 photolithography and is still in standard use. 



The first photolithographic halftones in the United States were 

 produced by Cutting and Bradford in 1856, although their patent was 

 dated 1858. The stone or grained zinc was coated with a solution of 

 gum arable, potassium bichromate, and sugar, exposed in the camera 

 or under a negative, and developed with a solution of soap. It was 

 then inked and printed. 



In 1857 Asser developed his photolitho transfer process, patented 

 in 1860, and took the first forward step in the medium since Poitevin. 

 This involved tlie sensitizing of sized paper Avith potassium-bichromate 

 solution, exposing under a negative, developing the paper, and inking 

 it. The image was then transferred to stone or zinc and printed. 

 Later workers made extensive use of the transfer method, which was 

 useful, among other things, in eliminating unnecessary handling of 

 the heavy stones. 



Developing Talbot's ideas, A. J. Berchtold suggested in 1855 and 

 1857 a variety of methods for producing screens. These included the 

 interposition of a transparent paper ruled with crossed lines between 

 the negative and the sensitized printing plate. Another interesting 

 idea, set forth in his French patent of 1857, was to cover a glass plate 

 with an opaque varnish and rule lines across it, which would remove 

 the varnish at equal intervals and create a series of fine transparent 

 parallel lines. This screen could then be placed over the photographic 

 image and exposed for as long a time as that which produced the 



