414 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1951 



image. The screen was then to be turned at right angles to the orig- 

 inal direction of the lines and the exposure continued, with less time 

 given for the second exposure. The screen was then to be turned 

 diagonally and exposed for a period of still less duration, and a 

 fourth turning on the opposite diagonal would be shortest of all. 

 Berchtold stated that the tones in the darkest areas would be composed 

 of four lines, the next darkest three, two, and one, supplemented as 

 well by dots where the lines intersected. This process, he stated, 

 would reproduce the modeling of the original photograph and could 

 be used for work in relief or typographic printing, gravure, or lith- 

 ography. Many of his suggestions, which we cannot be sure he him- 

 self ever developed, were worked out eventually by later experimenters. 



The first workable halftone screen was patented in 1865 in this 

 country by General Frederick von Egloffstein, who also founded the 

 Heliographic Engraving Co., the fii*st commercial establishment in 

 the United States for producing photomechanical halftones. Only 

 Paul Pretsch's Photogalvanographic Co. of London antedated von 

 Egloffstein's organization in the commercial field. 



In his patent of 1865 von Egloffstein described his screen, or "helio- 

 graphic and photographic spectrum for producing line-engravings," 

 as being a sheet of plate glass covered with an asphaltum grotind, as 

 used in the making of etchings. A diamond point governed by a rul- 

 ing machine was then traced over the dark ground, removing the 

 ground and creating transparent lines. A variety of patterns could 

 be traced, running from perfect parallelism to semicircular rhythms. 

 Von Egloffstein's typical screen, however, was a wavy single-line 

 effect made up of minute dashes. These screens were often extremely 

 fine, sometimes running to over 400 lines to the inch. Von Egloffstein 

 exposed his sensitized plate under a screen. His patent describes the 

 procedure as follows : 



The spectrum is thus imprinted upon the varnish previous to its receiving the 

 photographic image by means of a second exposure to the light. Both images 

 are thus blended into one, the spectrum giving texture to the photographic image. 

 Then may follow the ordinary heliographic manipulations of developing the 

 picture. The photograpliic image being the last, and for a longer period ex- 

 posed, overpowers the spectral image, but only so far as to preserve the delicate 

 half-tints, the spectrum remaining sufficiently strong to serve as a means for 

 holding printer's ink when impressions are taken from the plate. 



Von Egloffstein sometimes combined two or more screens, and an 

 examination of his halftones under a glass often reveals a complex 

 pattern of lines, dots, and dashes. His work was exceptionally good, 

 but because of his highly exclusive and secretive workshop practices 

 his business did not prosper. Von Egloffstein never allowed work- 

 men from one section of his shop to visit another section, fearing that 

 the details of his processes would become known and that others might 

 glean the fruits of his labors. 



