Photocopying
The term photocopying refers to the duplication of an existing document by using light. There are three major types of photocopying: photographic copying, which uses photographic techniques to develop copies on photosensitive materials; thermography, which is a dry-copying process that uses the action of heat on heat-sensitive chemicals; and xerography, which uses electrostatic charges, dry ink, and heat to fuse an image onto paper.
Although the process of photocopying is commonly thought to be a recent invention, the foundation for modern photocopying was laid before the nineteenth century. In 1780 the Scottish engineer and inventor James Watt took out a patent on a letter-copying machine after becoming frustrated with the inefficiency of making hand written copies of letters. The device consisted of a roller press which created a reverse impression on the copy paper. The paper which was used in this process was thin enough that the document could be read from left to right on the other side. The first models of the copying press were in great demand until the last quarter of the nineteenth century. In 1877 Thomas Alva Edison developed a stencil machine that squeezed ink onto to a type of wax paper. The only improvement that Edison made on Watt's copying machine was that the document was copied on the correct side and no longer had to be read through the paper. Edison's model was improved on by David Gestetner, who introduced the Cyclostyle pen which consisted of a spiked wheel pen that created perforations in the stencil. Next came the mimeograph; developed by A. B. Dick in 1884, this is commonly referred to as the ditto method.
In a parallel development to the early stencil devices, copy cameras were used to duplicate documents beginning in the early 1800s. Contact photocopying, one of the first camera-based copying devices, used lights and developers such as ammonia vapor or water to produce copies. Contact photocopying is still used to create blueprints. Microfilm was developed in 1839 by John Danzer. Danzer substituted a microscope lens for the regular lens in a camera. When microfilming, documents are imaged on a very small area of silver halide film. Fine-grain films and special lenses allow documents to be filmed at reduction ratios. The films are then contained in a retrieval magazine. If paper documents are discarded after microfilming, users can obtain large file space savings. Microfilm is used mostly for the archival and retrieval of documents. It is the second most common photocopying technique used today, and is a very efficient method for libraries and large companies.
Carl Miller invented the dry-copying method of thermography in 1944. He was inspired when he observed that snow melted under fallen leaves more quickly than in open air. This concept of heat absorption by a dark surface led to research in the 3M labs in Minnesota. 3M called its thermographic copier the Thermofax. Thermography allows infrared rays to produce a copy directly onto specially treated, thermo-sensitive paper without using a negative.
This is the most efficient and a more advanced method of photocopying. The word xerox comes from the Greek xeros, meaning dry, and graphein meaning to write. Today, photocopying is sometimes called xeroxing in the business world. Xerography depends upon the use of photoconducting metals, such as selenium, which conduct electricity only when exposed to light. A xerographic copying machine has a metal sheet coated with a photoconducting material that has a negative charge at the beginning of the copying cycle. Light is reflected off the white areas of the original document onto the coated metal. The electric charge disappears where light from the reflection strikes the coated metal surface, so only dark parts of the image remain charged. Positively charged particles of toner powder (dry ink) are applied to the metal surface. The charged parts of the metal surface attract the dark powder, which is transferred to paper. High temperatures seal the powder to the paper, and a xerographic copy is produced.
Xerography was developed by the American inventor Chester Carlson in 1938. Carlson developed the basic principles of the first electrostatic copier while doing experiments in the kitchen of his New York apartment. For a number of years he encountered difficulty in finding a company interested in his invention. In 1947 a small photo company, Haloid, agreed to develop the copier. The company eventually changed its name to Xerox and marketed its first machine, the Xerox 914, in 1959. Since Carlson's model, the xerox machine (photocopier) has been significantly improved. The copiers have increased speed and the ability to produce two-sided copies from single-sided originals, and reduced or enlarged copies. They can even collate the papers into packets and staple them. Color photocopiers became common in the 1980s and 1990s. They worked essentially the same way as black and white copiers, only the exposure and toner steps are repeated three times, and special filters and toners are involved to produce full-color.
In the 1990s, digital photocopiers became widely available. Photocopiers also became enhanced; multifunction photocopiers also worked as scanners, fax machines and printers, all in the same unit. In 1997, the Xerox company announced the development of digital copiers that can be linked to personal computers, and with special software, can output documents from anywhere on a network, and in the future, from the Internet. Thus, an original is not needed to make a copy; the photocopier handles both. The future of photocopiers also includes such items as the Recycle Copier, which can photocopy and reverse the process and strip a photocopy of its text, allowing a piece of paper to be used up to ten times. Another enhanced photocopier can automatically translate a document from English to Japanese. In the twenty-first century, photocopiers will continue to merge with printing and computer technologies into do-it-all machines.
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