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Xerography is a dry
photocopying A photocopier (also called copier or copy machine, and formerly Xerox machine, the generic trademark) is a machine that makes copies of documents and other visual images onto paper or plastic film quickly and cheaply. Most modern photocopier ...
technique. Originally called electrophotography, it was renamed xerography—from the
roots A root is the part of a plant, generally underground, that anchors the plant body, and absorbs and stores water and nutrients. Root or roots may also refer to: Art, entertainment, and media * ''The Root'' (magazine), an online magazine focusing ...
el, ξηρός, label=none ''xeros'', meaning "dry" and -γραφία ''-graphia'', meaning "writing"—to emphasize that unlike reproduction techniques then in use such as
cyanotype The cyanotype (from Ancient Greek κυάνεος - ''kuáneos'', “dark blue” + τύπος - ''túpos'', “mark, impression, type”) is a slow-reacting, economical photographic printing formulation sensitive to a limited near ultraviolet ...
, the process of xerography used no liquid
chemical A chemical substance is a form of matter having constant chemical composition and characteristic properties. Some references add that chemical substance cannot be separated into its constituent elements by physical separation methods, i.e., w ...
s.


History

Xerography was invented by American physicist
Chester Carlson Chester Floyd Carlson (February 8, 1906 – September 19, 1968) was an American physicist, inventor, and patent attorney born in Seattle, Washington. Carlson invented electrophotography, the process used by millions of photocopiers worldwide. C ...
, based significantly on contributions by Hungarian physicist
Pál Selényi Engineer Pál Selényi (17 November 1884 – 21 March 1954) "Fizikai Szemle 1999/5 - Zsolt Bor: OPTICS BY HUNGARIANS" (with Pál Selényi), József Attila University, Szeged, Hungary, 1999, webpage: KFKI-Hungary-Bor was known as the ...
. Carlson applied for and was awarded on October 6, 1942. Carlson's innovation combined electrostatic printing with
photography Photography is the art, application, and practice of creating durable images by recording light, either electronically by means of an image sensor, or chemically by means of a light-sensitive material such as photographic film. It is emplo ...
, unlike the dry
electrostatic Electrostatics is a branch of physics that studies electric charges at rest ( static electricity). Since classical times, it has been known that some materials, such as amber, attract lightweight particles after rubbing. The Greek word for ...
printing Printing is a process for mass reproducing text and images using a master form or template. The earliest non-paper products involving printing include cylinder seals and objects such as the Cyrus Cylinder and the Cylinders of Nabonidus. The ...
process invented by
Georg Christoph Lichtenberg Georg Christoph Lichtenberg (1 July 1742 – 24 February 1799) was a German physicist, satirist, and Anglophile. As a scientist, he was the first to hold a professorship explicitly dedicated to experimental physics in Germany. He is remembered for ...
in 1778. Carlson's original process was cumbersome, requiring several manual processing steps with flat plates. In 1946, Carlson signed an agreement with Haloid Photographic Company to develop it as a commercial product. Before that year, Carlson had proposed his idea to more than a dozen companies, but none was interested. Haloid's president,
Joseph C. Wilson Joseph Charles Wilson IV (November 6, 1949 – September 27, 2019) was an American diplomat who was best known for his 2002 trip to Niger to investigate allegations that Saddam Hussein was attempting to purchase yellowcake uranium; his ''New Y ...
, saw the promise of Carlson's invention, and saw to it that Haloid diligently worked to produce a working commercial product. It was almost 18 years before a fully automated process was developed, the key breakthrough being the use of a
cylindrical A cylinder (from ) has traditionally been a three-dimensional solid, one of the most basic of curvilinear geometric shapes. In elementary geometry, it is considered a prism with a circle as its base. A cylinder may also be defined as an in ...
drum coated with
selenium Selenium is a chemical element with the symbol Se and atomic number 34. It is a nonmetal (more rarely considered a metalloid) with properties that are intermediate between the elements above and below in the periodic table, sulfur and tellurium, ...
instead of a flat plate. This resulted in the first commercial automatic copier, the
Xerox 914 The Xerox 914 was the first successful commercial photocopying, plain paper copier. Introduced in 1959 by the Xerox, Haloid/Xerox company. It revolutionized the document-copying industry. The culmination of inventor Chester Carlson's work on the ...
, being released by Haloid/Xerox in 1960. Xerography is now used in most
photocopying A photocopier (also called copier or copy machine, and formerly Xerox machine, the generic trademark) is a machine that makes copies of documents and other visual images onto paper or plastic film quickly and cheaply. Most modern photocopier ...
machines and in
laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The ...
and
LED printer An LED printer is a type of computer printer similar to a laser printer. Such a printer uses a light-emitting diode (LED) array as a light source in the printhead instead of the laser used in laser printers and, more generally, in the xerograp ...
s.


Process

The first commercial use was hand processing of a flat photosensor (an electrostatic component that detects the presence of visible light) with a copy camera and a separate processing unit to produce offset lithographic plates. Today this technology is used in photocopy machines,
laser printer Laser printing is an electrostatic digital printing process. It produces high-quality text and graphics (and moderate-quality photographs) by repeatedly passing a laser beam back and forth over a negatively-charged cylinder called a "drum" to ...
s, and
digital press Digital printing is a method of printing from a digital-based image directly to a variety of media. It usually refers to professional printing where small-run jobs from desktop publishing and other digital sources are printed using large-format ...
es which are slowly replacing many traditional offset presses in the printing industry for shorter runs. By using a cylinder to carry the photosensor, automatic processing was enabled. In 1960, the automatic
photocopier A photocopier (also called copier or copy machine, and formerly Xerox machine, the generic trademark) is a machine that makes copies of documents and other visual images onto paper or plastic film quickly and cheaply. Most modern photocopier ...
was created and many millions have been built since. The same process is used in
microform Microforms are scaled-down reproductions of documents, typically either films or paper, made for the purposes of transmission, storage, reading, and printing. Microform images are commonly reduced to about 4% or of the original document size. ...
printers and computer output
laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The ...
or
LED printer An LED printer is a type of computer printer similar to a laser printer. Such a printer uses a light-emitting diode (LED) array as a light source in the printhead instead of the laser used in laser printers and, more generally, in the xerograp ...
s. A metal cylinder called the drum is mounted to rotate about a horizontal axis. The drum rotates at the speed of paper output. One revolution passes the drum surface through the steps described below. The end-to-end dimension is the width of print to be produced plus a generous tolerance. The drums in the copiers originally developed by
Xerox Corporation Xerox Holdings Corporation (; also known simply as Xerox) is an American corporation that sells print and digital document products and services in more than 160 countries. Xerox is headquartered in Norwalk, Connecticut (having moved from St ...
were manufactured with a surface coating of
amorphous In condensed matter physics and materials science, an amorphous solid (or non-crystalline solid, glassy solid) is a solid that lacks the long-range order that is characteristic of a crystal. Etymology The term comes from the Greek language, Gr ...
selenium Selenium is a chemical element with the symbol Se and atomic number 34. It is a nonmetal (more rarely considered a metalloid) with properties that are intermediate between the elements above and below in the periodic table, sulfur and tellurium, ...
(more recently ceramic or organic photoconductor or OPC), applied by vacuum deposition. Amorphous selenium will hold an electrostatic charge in darkness and will conduct away such a charge under light. In the 1970s, IBM Corporation sought to avoid Xerox's patents for selenium drums by developing organic photoconductors as an alternative to the selenium drum. In the original system, photocopiers that rely on silicon or selenium (and its alloys) are charged positively in use (hence work with negatively-charged "toner" powder). Photoconductors using organic compounds are electrochemically charged vice versa to the preceding system in order to exploit their native properties in printing."Photocopying processes". ''McGraw-Hill Encyclopedia of Science and Technology'' vol. 13, p. 395, 10th edition, 2007 Organic photoconductors are now preferred because they can be deposited on a flexible, oval or triangular, belt instead of a round drum, facilitating significantly smaller device build size. Laser printer photo drums are made with a doped
silicon diode A diode is a two- terminal electronic component that conducts current primarily in one direction (asymmetric conductance); it has low (ideally zero) resistance in one direction, and high (ideally infinite) resistance in the other. A diode ...
sandwich structure with a hydrogen-doped silicon light-chargeable layer, a boron
nitride In chemistry, a nitride is an inorganic compound of nitrogen. The "nitride" anion, N3- ion, is very elusive but compounds of nitride are numerous, although rarely naturally occuring. Some nitrides have a find applications, such as wear-resistant ...
rectifying (diode-causing) layer that minimizes current leakage, and a surface layer of silicon doped with oxygen or nitrogen; silicon nitride is a scuff-resistant material. The steps of the process are described below as applied on a cylinder, as in a photocopier. Some variants are described within the text. Every step of the process has design variants. The physics of the xerographic process are discussed at length in a book. ; Step 1. Charging An
electrostatic Electrostatics is a branch of physics that studies electric charges at rest ( static electricity). Since classical times, it has been known that some materials, such as amber, attract lightweight particles after rubbing. The Greek word for ...
charge of −600
volts The volt (symbol: V) is the unit of electric potential, electric potential difference (voltage), and electromotive force in the International System of Units (SI). It is named after the Italian physicist Alessandro Volta (1745–1827). Defini ...
is uniformly distributed over the surface of the drum by a
corona discharge A corona discharge is an electrical discharge caused by the ionization of a fluid such as air surrounding a conductor carrying a high voltage. It represents a local region where the air (or other fluid) has undergone electrical breakdown ...
from a corona unit (Corotron), with output limited by a control grid or screen. This effect can also be achieved with the use of a contact roller with a charge applied to it. Essentially, a corona discharge is generated by a very thin wire to  inch (6.35 to 12.7 mm) away from the photoconductor. A
negative charge Electric charge is the physical property of matter that causes charged matter to experience a force when placed in an electromagnetic field. Electric charge can be ''positive'' or ''negative'' (commonly carried by protons and electrons respectiv ...
is placed on the wire, which will ionize the space between the wire and conductor, so
electrons The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have n ...
will be repelled and pushed away onto the conductor. The conductor is set on top of a conducting surface, kept at ground potential.Photocopying processes". ''McGraw-Hill Encyclopedia of Science and Technology'' vol. 13, p. 394, 10th edition, 2007 The polarity is chosen to suit the positive or negative process. Positive process is used for producing black on white copies. Negative process is used for producing black on white from negative originals (mainly microfilm) and all digital printing and copying. This is to economize on the use of laser light by the "blackwriting" or "write to black" exposure method. ; Step 2. Exposure The document or microform to be copied is illuminated by flash lamps on the platen and either passed over a lens or is scanned by a moving light and lens, such that its image is projected onto and synchronized with the moving drum surface. Alternatively, the image may be exposed using a xenon strobe onto the surface of the moving drum or belt, fast enough to render a perfect latent image. Where there is text or image on the document, the corresponding area of the drum will remain unlit. Where there is no image the drum will be illuminated and the charge will be dissipated. The charge that remains on the drum after this exposure is a 'latent' image and is a negative of the original document. Whether in a scanning or a stationary optical system, combinations of lenses and mirrors are used to project the original image on the platen (scanning surface) onto the photoconductor. Additional lenses, with different focal lengths or zooming lenses are utilized to enlarge or reduce the image. The scanning system, though, must change its scanner speed to adapt to elements or reductions. A drum is inferior to a belt in the sense that although it is simpler than a belt, it must be buffered gradually in parts rolling on the drum. As a result, the belt is more efficient to use one exposure to make a direct passage. In a laser or LED printer, modulated light is projected onto the drum surface to create the latent image. The modulated light is used only to create the positive image, hence the term "blackwriting". ; Step 3. Development In high-volume copiers, the drum is presented with a slowly turbulent mixture of toner particles and larger, iron, reusable carrier particles. Toner is a powder; its early form was carbon powder, then melt-mixed with a polymer. The carrier particles have a coating which, during agitation, generates a
triboelectric The triboelectric effect (also known as triboelectric charging) is a type of contact electrification on which certain materials become electrically charged after they are separated from a different material with which they were in contact. Rub ...
charge (a form of static electricity), which attracts a coating of toner particles. In addition, the mix is manipulated with a magnetic roller to present to the surface of the drum or belt a brush of toner. By contact with the carrier each neutral toner particle has an electric charge of polarity opposite to the charge of the latent image on the drum. The charge attracts toner to form a visible image on the drum. To control the amount of toner transferred, a bias voltage is applied to the developer roller to counteract the attraction between toner and latent image. Where a negative image is required, as when printing from a microform negative, then the toner has the same polarity as the corona in step 1. Electrostatic lines of force drive the toner particles away from the latent image towards the uncharged area, which is the area exposed from the negative. Early color copiers and printers used multiple copy cycles for each page output, using colored filters and toners. Modern units use only a single scan to four separate, miniature process units, operating simultaneously, each with its own coronas, drum and developer unit. ; Step 4. Transfer Paper is passed between the drum and the transfer corona, which has a polarity that is the opposite of the charge on the toner. The toner image is transferred from the drum to the paper by a combination of pressure and electrostatic attraction. On many color and high-speed machines, it is common to replace the transfer corona with one or more charged bias transfer rollers, which apply greater pressure and produce a higher quality image. ; Step 5. Separation or detack Electric charges on the paper are partially neutralized by AC from a second corona, usually constructed in tandem with the transfer corona and immediately after it. As a result, the paper, complete with most (but not all) of the toner image, is separated from the drum or belt surface. ; Step 6. Fixing or fusing The toner image is permanently fixed to the paper using either a heat and pressure mechanism (hot roll fuser) or a radiant fusing technology (oven fuser) to melt and bond the toner particles into the medium (usually paper) being printed. There also used to be available "offline" vapor fusers. These were trays covered in cotton gauze sprinkled with a volatile liquid, such as ether. When the transferred image was brought into proximity with the vapor from the evaporating liquid, the result was a perfectly fixed copy without any of the distortion or toner migration which can occur with the other methods. This method is no longer used due to emissions of fumes. ; Step 7. Cleaning The drum, having already been partially discharged during detack, is further discharged by light. Any remaining toner, that did not transfer in step 6, is removed from the drum surface by a rotating brush under suction, or a squeegee known as the cleaning blade. This 'waste' toner usually is routed into a waste toner compartment for later disposal; however, in some systems, it is routed back into the developer unit for reuse. This process, known as toner reclaim, is much more economical, but can possibly lead to a reduced overall toner efficiency through a process known as 'toner polluting' whereby concentration levels of toner/developer having poor electrostatic properties are permitted to build up in the developer unit, reducing the overall efficiency of the toner in the system. Some systems have abandoned the separate developer (carrier). These systems, known as monocomponent, operate as above, but use either a magnetic toner or fusible developer. There is no need to replace worn-out developer, as the user effectively replaces it along with the toner. An alternative developing system, developed by KIP from an abandoned line of research by Xerox, completely replaces magnetic toner manipulation and the cleaning system, with a series of computer-controlled, varying biases. The toner is printed directly onto the drum, by direct contact with a rubber developing roller which, by reversing the bias, removes all the unwanted toner and returns it to the developer unit for reuse. The development of xerography has led to new technologies that have the potential to eventually eradicate traditional
offset printing Offset printing is a common printing technique in which the inked image is transferred (or "offset") from a plate to a rubber blanket and then to the printing surface. When used in combination with the lithographic process, which is based on ...
machines. These new machines that print in full
CMYK The CMYK color model (also known as process color, or four color) is a subtractive color model, based on the CMY color model, used in color printing, and is also used to describe the printing process itself. The abbreviation ''CMYK'' refers ...
color, such as Xeikon, use xerography but provide nearly the quality of traditional ink prints.


Durability

Xerographic documents (and the closely related laser printer printouts) can have excellent archival durability, depending on the quality of the paper used. If low-quality paper is used, it can yellow and degrade due to residual
acid In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a se ...
in the untreated pulp; in the worst case, old copies can literally crumble into small particles when handled. High-quality xerographic copies on
acid-free paper Acid-free paper is paper that, if infused in water, yields a neutral or basic pH (7 or slightly greater). It can be made from any cellulose fiber as long as the active acid pulp is eliminated during processing. It is also lignin- and sulfur-fre ...
can last as long as typewritten or handwritten documents on the same paper. However, xerographic copies are vulnerable to undesirable toner transfer if they are stored in direct contact or close proximity to
plasticizer A plasticizer ( UK: plasticiser) is a substance that is added to a material to make it softer and more flexible, to increase its plasticity, to decrease its viscosity, and/or to decrease friction during its handling in manufacture. Plasticiz ...
s, which are present in looseleaf binders made with PVC. In extreme cases, the ink toner will stick directly to the binder cover, pulling away from the paper copy and rendering it illegible.


Uses in animation

Ub Iwerks Ubbe Ert Iwwerks (March 24, 1901 – July 7, 1971), known as Ub Iwerks ( ), was an American animator, cartoonist, character designer, inventor, and special effects technician. Born in Kansas City, Missouri, Iwerks grew up with a contentiou ...
adapted xerography to eliminate the hand-inking stage in the animation process by printing the animator's drawings directly to the cels. The first animated feature film to use this process was '' One Hundred and One Dalmatians'' (1961), although the technique was already tested in ''
Sleeping Beauty ''Sleeping Beauty'' (french: La belle au bois dormant, or ''The Beauty in the Sleeping Forest''; german: Dornröschen, or ''Little Briar Rose''), also titled in English as ''The Sleeping Beauty in the Woods'', is a fairy tale about a princess cu ...
'', released two years earlier. At first, only black lines were possible, but in 1977, gray lines were introduced and used in '' The Rescuers'' and in the 1980s, colored lines were introduced and used in animated features like '' The Secret of NIMH''.


Uses in art

Xerography has been used by photographers internationally as a direct imaging photographic process, by book artists for publishing one-of-a-kind books or multiples, and by collaborating artists in portfolios such as those produced by the International Society of Copier Artists founded by American Louise Odes Neaderland. Art critic Roy Proctor said of artist/curator Louise Neaderland during her residency for the exhibition ''Art ex Machina'' at 1708 Gallery in Richmond, Virginia, "She's living proof that, when a new technology begins to be mass-produced, artists will be curious enough—and imaginative enough—to explore its creative uses.


References


Further reading

* * *Eichhorn, Kate (2016). Adjusted Margin: Xerography, Art, and Activism in the Late Twentieth Century. Cambridge: The MIT Press.


External links


"Static Pops Pictures On Paper"
detailed 1949 ''
Popular Science ''Popular Science'' (also known as ''PopSci'') is an American digital magazine carrying popular science content, which refers to articles for the general reader on science and technology subjects. ''Popular Science'' has won over 58 awards, incl ...
'' article on the history and technology of xerography {{Authority control 1938 introductions Non-impact printing Electrostatics American inventions Xerox art