Other Free Encyclopedias » Science Encyclopedia » Science & Philosophy: Philosophy of Mind - Early Ideas to Planck length » Photocopying - Xerography, Addition Of Toner And Fusing, Color Copying, Electrostatic Copying, Thermography, Diazo Copying

Photocopying - Diazo Copying

paper surface light document

Diazo copying gets its name from the fact that it makes use of copy paper that has been treated with a type of chemical known as diazonium compounds. As with the thermographic process described above, diazonium compounds change color when exposed to heat. In diazo copying, the original document and the diazotreated copy paper are placed in contact with each other in a light box and then exposed to a strong source of ultraviolet light. Dark regions on the original document become warm, causing corresponding areas on the diazo paper to darken. The color in these regions is brought about by exposing the copy paper to a developing agent such as ammonia gas. Blue-printing and brown-printing are specialized kinds of diazo copying.



Considine, Glenn D. Van Nostrand's Scientific Encyclopedia. New York: Wiley-Interscience, 2002.

Macaulay, David. The New Way Things Work. Boston: Houghton Mifflin Company, 1998.

Mort, J. The Anatomy of Xerography: Its Invention and Evolution. Jefferson, NC: McFarland, 1989.

Trefil, James. Encyclopedia of Science and Technology. The Reference Works, Inc., 2001.

David E. Newton


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Copy paper

—Plain or treated paper on which the image of an original document is produced in a copy machine.

Corona bar

—A device used to add an electrical charge to a surface, given that name because a pale blue light (a "corona") often surrounds the device.

Diazo copying

—A copying process that makes use of changes in certain chemical compounds (diazonium compounds) when heat is added to them.

Electrostatic copying

—A copying process similar to xerography, but somewhat simpler in its procedure and requiring a specially-treated copy paper.

Photoconducting surface

—Any kind of surface on which a copy of a document can be made using light as the copying medium.


—A type of photocopying in which portions of specially treated copy paper darken as a result of being exposed to heat.


—A material that carries an electrical charge opposite to that of a photoconducting surface that is added to that surface in a copy machine.


—A type of photocopying that makes use of an endless photocopying surface to record light and dark areas in an original document as charged or uncharged areas on a photoconducting surface.

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