bichromated+gum

SUBJECT AREA: Photography, film and optics

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Educated at Harrow, where he first showed an interest in science, and at Cambridge, Talbot was an outstanding scholar and a formidable mathematician. He published over fifty scientific papers and took out twelve English patents. His interests outside the field of science were also wide and included Assyriology, etymology and the classics. He was briefly a Member of Parliament, but did not pursue a parliamentary career.

Talbot's invention of photography arose out of his frustrating attempts to produce acceptable pencil sketches using popular artist's aids, the camera discura and camera lucida. From his experiments with the former he conceived the idea of placing on the screen a paper coated with silver salts so that the image would be captured chemically. During the spring of 1834 he made outline images of subjects such as leaves and flowers by placing them on sheets of sensitized paper and exposing them to sunlight. No camera was involved and the first images produced using an optical system were made with a solar microscope. It was only when he had devised a more sensitive paper that Talbot was able to make camera pictures; the earliest surviving camera negative dates from August 1835. From the beginning, Talbot noticed that the lights and shades of his images were reversed. During 1834 or 1835 he discovered that by placing this reversed image on another sheet of sensitized paper and again exposing it to sunlight, a picture was produced with lights and shades in the correct disposition. Talbot had discovered the basis of modern photography, the photographic negative, from which could be produced an unlimited number of positives. He did little further work until the announcement of Daguerre's process in 1839 prompted him to publish an account of his negative-positive process. Aware that his photogenic drawing process had many imperfections, Talbot plunged into further experiments and in September 1840, using a mixture incorporating a solution of gallic acid, discovered an invisible latent image that could be made visible by development. This improved calotype process dramatically shortened exposure times and allowed Talbot to take portraits. In 1841 he patented the process, an exercise that was later to cause controversy, and between 1844 and 1846 produced The Pencil of Nature, the world's first commercial photographically illustrated book.

Concerned that some of his photographs were prone to fading, Talbot later began experiments to combine photography with printing and engraving. Using bichromated gelatine, he devised the first practicable method of photo engraving, which was patented as Photoglyphic engraving in October 1852. He later went on to use screens of gauze, muslin and finely powdered gum to break up the image into lines and dots, thus anticipating modern photomechanical processes.

Talbot was described by contemporaries as the "Father of Photography" primarily in recognition of his discovery of the negative-positive process, but he also produced the first photomicrographs, took the first high-speed photographs with the aid of a spark from a Leyden jar, and is credited with proposing infra-red photography. He was a shy man and his misguided attempts to enforce his calotype patent made him many enemies. It was perhaps for this reason that he never received the formal recognition from the British nation that his family felt he deserved.

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