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The term photostat machine is often used to describe any kind of machine that can make duplicates of text or graphic documents. Modern photocopiers, using techniques first introduced commercially by the Xerox company in the 1950s, are sometimes called photostat machines. This usage is incorrect, however. A true photostat machine is another type of document duplicating device, developed simultaneously in the early 20th century by two American companies. The name photostat comes from the name of one of the companies, Photostat, which was a division of the Eastman-Kodak company.
Although the term photostat is still sometimes used today as a generic term to describe any copy machine, true photostat machines are today generally found only in museums. Document duplication technology has been developed along several lines of research since medieval times, beginning with the Gutenberg printing press. A photostat machine is a type of machine that was developed using photography as a method for reproducing documents.
At the beginning of the 20th century, photography using film was a relatively new advancement, having first been introduced by George Eastman in 1884. Prior to that, photography was carried out using a photographic plate. Exposing film during the process of taking a picture resulted in a negative image, where the shading was reversed from actual conditions. The negative was then used to create a print which reversed this shading, producing a true-to-life image.
Photostat machines used this principle to create duplicates of documents. Text, as well as illustrations or even photographs, could be reproduced this way. The main component of the photostat machine was a camera which the operator used to take a picture of the document to be copied. Instead of photographic film, however, the negative image was exposed directly onto sensitized paper, which was loaded into the machine in the form of a long roll. This was then developed like a regular photograph by immersion in a series of chemical baths.
This negative image was called a black print, as a standard typed letter photographed in this way would result in a black page with white lettering. When this black print was dry, it was then re-photographed, using the same sensitized paper. The result would be a negative of the black print, which would again resemble a typical document page of black lettering on white paper. As many copies as were desired could be created this way by repeatedly photographing the black print and developing the resulting photographs on the special paper. Photostat machines were bulky, expensive, and slow compared to modern copiers, and with the introduction of the Xerox® process in the 1950s, the photostat machine quickly disappeared.