photoresist, which was developed and chemically etched, a process known as photoengraving and already in use for making printing plates from line drawings, handwriting and other purely black and white subject matter. Although complex, this process was simpler and more efficient than other processes then in some limited use, and in 1884 Ives asserted that it was "the first patented or published process which was introduced into truly successful commercial operation." A few years later, Ives replaced this process with the much simpler one usually associated with his name. In the new process, an ordinary photograph was rephotographed directly onto the sensitized metal plate. A crossline screen, consisting of two glass plates finely ruled with opaque lines and sandwiched together with their lines crossing at right angles, was positioned near the surface of the metal, and a specially shaped diaphragm was used with the camera lens. Combined with the inherently stark black-and-white nature of the photoengraving process, these devices served to break up the image into a regular pattern of dots of various sizes with optimized shapes. During the 1890s, photographs reproduced by this second "Ives process" largely replaced the use of hand-engraved wood block and steel plate illustrations. It remained the standard process for photographically illustrating books, magazines and newspapers during the next eighty years. Although much more technologically sophisticated methods eventually came into use for creating the printing plates, the structure of most printed halftone images has remained virtually unchanged. References External links Ives papers at the Smithsonian 1856 births 1937 deaths American inventors People from Litchfield, Connecticut American photographers