420 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1951 



to bridge the gap between theory and practice. Garside and Borland, 

 in their separate British patents of 1883, had suggested screens to be 

 placed some distance away from the negative. It is evident that they 

 had no notion that a proper focus was necessary, and nothing came 

 of their patents. 



The crowning achievement in halftone screens was the Levy prod- 

 uct, which has been unsurpassed from about 1890 to the present day. 

 Although Ives had cemented screens together somewhat earlier, his 

 screens were of the old variety, ruled by a diamond point through 

 darkened collodion coatings. It was the Levys who created a new 

 type of screen, made of the finest optical glass, on which dark lines 

 appeared on a transparent ground. The glass was first coated with 

 an acid-resisting substance. An improved automatic ruling machine, 

 invented by Max Levy, made use of a diamond point in cutting the 

 desired number of lines to the inch on this surface. The fum.es of 

 hydrofluoric acid were then used to etch the lines in the glass. After 

 the resist was removed, the lines were defined by filling them w^ith a 

 black substance. Two single-line screens were then cemented together 

 so that the lines formed right angles, creating a cross-lined screen. 

 This method, in its essentials, is still used today. 



The Levys' first important patent was granted in 1893, although 

 their screens had been on the market since about 1890. In any case 

 their screens were of such fine quality, so apparently flawless in work- 

 manship, that no other company has been able to dislodge them from 

 their position of preeminence. During the early period, in particu- 

 lar, they were almost without competitors. 



The matter of manufacturing halftone screens is far more difficult 

 than it might appear. Glass does not often etch cleanly, and ruling 

 200 to 400 flawless lines to the inch through asphaltum coatings with a 

 diamond point requires special knowledge and special equipment. 

 Until recently the Levy processes were kept secret. While others 

 tried to manufacture screens of comparable quality, they were unable 

 for many years to do so, and Levy screens became synonymous with 

 the finest work in halftone. 



The old photogravure process, invented by Fox Talbot in 1852, had 

 in the meantime risen to first rank among the tonal printing processes, 

 at least from the standpoint of quality. It was universally conceded 

 to be the most "artistic" printing process, and in fact it produced 

 prints of an unequaled richness and beauty of tone. However, this 

 process required more hand work than any other method, and conse- 

 quently it was also the slowest and most expensive printing method. 

 Nevertheless, it produced such magnificent results that it was widely 

 employed, both for special plates to be tipped into publications and 

 for reproducing paintings and other subjects for separate issue. 



