Contact copier

Last updated January 16, 2025

A contact copier (also known as contact printer) is a device used to copy an image by illuminating a film negative with the image in direct contact with a photosensitive surface (film, paper, plate, etc.). The more common processes are negative, where clear areas in the original produce an opaque or hardened photosensitive surface, but positive processes are available. The light source is usually an actinic bulb internal or external to the device^[1]

Commercial contact printers or process cameras usually use a pump-operated vacuum frame where the original and the photosensitive surface are pressed together against a flat glass by a grooved rubber mat connected to the vacuum source. A timer-controlled mercury vapor (arc or fluorescent) light source is on the other side of the glass.^[1]

Uses

The contact copying process was used in the early days of photography and sunlight-exposed blueprints; it is still used in amateur photography, silkscreen printing, offset printing, and photochemical machining, such as the manufacture of printed circuit boards. By the early 20th century, blueprinting (producing white lines) or diazo blue line printing used contact-rollers rather than flat-glass exposure.^{[ citation needed ]}

Silkscreen printing and photochemical machining originally were based on gum bichromate photosensitive materials, where exposure to intense ultraviolet light made previously-soluble gum or gelatin colloids insoluble; after exposure, the exposed surface was washed in water and the unexposed coating dissolved, leaving the hardened gum or gelatin to resist the passage of the silk-screen ink or the metal-etching solution. Offset printing can use either a negative plate, where the hardened, exposed photosensitive coating attracts ink and repels water, or a positive plate, where the exposed photosensitive coating decomposes or exposes the metal, water-attracting surface.

Photography

The contact copier is used for duplication of negative or positive prints obtaining what are called contact prints, that is, to reproduce on paper or film, a photographic negative or positive of exactly the same size of the original. (With normal photographic non inverting processes, black generates white on the target while white generates black). It was the common mode to make prints until it began the use of the alternative photographic enlarger. There are some models with internal light source constructed as a closed box, in which one or more lamps illuminate the negative through an opal or frosted glass.

The reproduction is done by placing the negative on top of the glass and then the photo paper with the emulsion in contact with the negative. The negative role fits the body, the lid is closed applying some pressure against the glass to prevent blur; then proceed to impress photographic paper by turning on the interior light (contact copier) or an external focus, in the last case, usually from a photographic enlarger. Exposure time can be controlled "manually" or using a timer that controls the light source for a preset time and with greater precision.

Whiteprint

In the process of whiteprint copying ,^[2] (essentially a diazotype process), a dynamic contact copier is used (similar to the manual action of exposing both sheets strongly bonded directly to the sunlight.). The exposition is made progressively as the twin rollers pull the two papers together (original and copy) against a source of ultraviolet light, typically a powerful black light lamp . The original plan (on a transparent support) and the diazo paper are introduced, in perfect contact, within the pinch rollers of the contact copier. The sensitized paper, has a photosensitive coating -an impregnation of diazo - covering the surface of the paper. Once exposed, the copied paper is immersed in a developer solution made from ammonia (or ammonia vapor) converting the parts of the paper not exposed to the light source to a characteristic dark violet colour (blue-line).

Silkscreen

In screenprinting it is normally use a contact copier box with several fluorescent tubes close to the silk frame. The emulsion reacts depending on the amount of light received, for that reason it is important to make some tests for determining the exposure time. Usually for a "box type" contact copier, exposure is usually not more than one minute. In the industrial type contact copiers with actinic lamp placed at a distance, exposure time can be about 20 minutes.

The photolith (also called "Art") is placed under the frame against the emulsion. The black portions of photolith film does not let light into the relevant parts of the coated silk, therefore, in these parts Emulsion will not heal and may be subsequently washed, keep in mind that there must be no gap between the photolith and the silk, to achieve that purpose any element with enough weight may be used to press the silk against the photolith (or a vacuum pump in professional machines).

Offset

In CTF offset technology, a photolith is placed in direct contact with the printing plate and pressed with an opaque lid that sometimes has a vacuum pump that helps making a good contact. The plate comes coated with a layer of photoresist in which a (negative) inverted image is formed with respect to the original photolith and after the transfer of information (burning) it's accomplished, then, after undergoing a developing process, the plate will be ready to be used in an offset printer.^[3]

The process shares some fundamental principles with the photographic processes, since the pattern engraved on the plate is generated by exposure to light with an image created in a contact copier using an optical mask. This procedure is comparable to the high-precision method of the version used to make printed circuit boards.

Printed circuits

The contact copier is used today, particularly in the areas hobbyist, for the photoengraving of prototype printed circuit boards (PCBs) before being sent to production (artisanal creation ). Substantially similar to the contact printer used in photography, this variant usually uses ultraviolet lamps to impress a copper base specifically pre-sensitized.

Burned by exposure to light parts reproduce patterns drawn on a transparent photolith film on a pre-sensitized plate (epoxy or Bakelite). This pre-sensitized plate comprises an insulating plate (epoxy resin or bakelite), adhered with a layer of copper, and coated with a varnish layer sensitized. The varnish is sensitive to UV rays, which weaken or strengthen its structure depending on whether a "positive" or "negative" process. Photolith film printed parts (usually black), inserted between the light source and the pre-sensitized plate, protect the varnish from the UV. The base copper impressed must then be engraved in a specific bath (usually ferric chloride FeCl₃), that removes the excess copper.

Related Research Articles

Lithography is a planographic method of printing originally based on the immiscibility of oil and water. The printing is from a stone or a metal plate with a smooth surface. It was invented in 1796 by the German author and actor Alois Senefelder and was initially used mostly for musical scores and maps. Lithography can be used to print text or images onto paper or other suitable material. A lithograph is something printed by lithography, but this term is only used for fine art prints and some other, mostly older, types of printed matter, not for those made by modern commercial lithography.

<span class="mw-page-title-main">Blueprint</span> Document reproduction by contact printing on light-sensitive sheets

A blueprint is a reproduction of a technical drawing or engineering drawing using a contact print process on light-sensitive sheets introduced by Sir John Herschel in 1842. The process allowed rapid and accurate production of an unlimited number of copies. It was widely used for over a century for the reproduction of specification drawings used in construction and industry. Blueprints were characterized by white lines on a blue background, a negative of the original. Color or shades of grey could not be reproduced.

The collodion process is an early photographic process. The collodion process, mostly synonymous with the "collodion wet plate process", requires the photographic material to be coated, sensitized, exposed, and developed within the span of about fifteen minutes, necessitating a portable darkroom for use in the field. Collodion is normally used in its wet form, but it can also be used in its dry form, at the cost of greatly increased exposure time. The increased exposure time made the dry form unsuitable for the usual portraiture work of most professional photographers of the 19th century. The use of the dry form was mostly confined to landscape photography and other special applications where minutes-long exposure times were tolerable.

The albumen print, also called albumen silver print, is a method of producing a photographic print using egg whites. Published in January 1847 by Louis Désiré Blanquart-Evrard, it was the first commercial process of producing a photo on a paper base from a negative, previous methods - such as the daguerreotype and the tintype - having been printed on metal. It became the dominant form of photographic positives from 1855 to the start of the 20th century, with a peak in the 1860–90 period. During the mid-19th century, the carte de visite became one of the more popular uses of the albumen method. In the 19th century, E. & H. T. Anthony & Company were the largest makers and distributors of albumen photographic prints and paper in the United States.

Color photography is photography that uses media capable of capturing and reproducing colors. By contrast, black-and-white or gray-monochrome photography records only a single channel of luminance (brightness) and uses media capable only of showing shades of gray.

Within the commercial printing industry, the job of stripping involves arranging and joining film negatives as part of the process of preparing printing plates. In the UK, the same operation is termed "planning" and film positives are used, rather than the negatives in the USA. Because the industry has largely moved to digital processes, the job of stripping, or planning has become rare or even obsolete.

The gelatin silver print is the most commonly used chemical process in black-and-white photography, and is the fundamental chemical process for modern analog color photography. As such, films and printing papers available for analog photography rarely rely on any other chemical process to record an image. A suspension of silver salts in gelatin is coated onto a support such as glass, flexible plastic or film, baryta paper, or resin-coated paper. These light-sensitive materials are stable under normal keeping conditions and are able to be exposed and processed even many years after their manufacture. The "dry plate" gelatin process was an improvement on the collodion wet-plate process dominant from the 1850s–1880s, which had to be exposed and developed immediately after coating.

An enlarger is a specialized transparency projector used to produce photographic prints from film or glass negatives, or from transparencies.

A contact print is a photographic image produced from film; sometimes from a film negative, and sometimes from a film positive or paper negative. In a darkroom an exposed and developed piece of film or photographic paper is placed emulsion side down, in contact with a piece of photographic paper, light is briefly shone through the negative or paper and then the paper is developed to reveal the final print.

Photographic printing is the process of producing a final image on paper for viewing, using chemically sensitized paper. The paper is exposed to a photographic negative, a positive transparency , or a digital image file projected using an enlarger or digital exposure unit such as a LightJet or Minilab printer. Alternatively, the negative or transparency may be placed atop the paper and directly exposed, creating a contact print. Digital photographs are commonly printed on plain paper, for example by a color printer, but this is not considered "photographic printing".

Photoengraving is a process that uses a light-sensitive photoresist applied to the surface to be engraved to create a mask that protects some areas during a subsequent operation which etches, dissolves, or otherwise removes some or all of the material from the unshielded areas of a substrate. Normally applied to metal, it can also be used on glass, plastic and other materials.

Whiteprint describes a document reproduction produced by using the diazo chemical process. It is also known as the blue-line process since the result is blue lines on a white background. It is a contact printing process that accurately reproduces the original in size, but cannot reproduce continuous tones or colors. The light sensitivity of the chemicals used was known in the 1890s and several related printing processes were patented at that time. Whiteprinting replaced the blueprint process for reproducing architectural and engineering drawings because the process was simpler and involved fewer toxic chemicals. A blue-line print is not permanent and will fade if exposed to light for weeks or months, but a drawing print that lasts only a few months is sufficient for many purposes.

A latent image is an invisible image produced by the exposure to light of a photosensitive material such as photographic film. When photographic film is developed, the area that was exposed darkens and forms a visible image. In the early days of photography, the nature of the invisible change in the silver halide crystals of the film's emulsion coating was unknown, so the image was said to be "latent" until the film was treated with photographic developer.

Sun printing may refer to various printing techniques which use sunlight as a developing or fixative agent.

Gum printing is a way of making photographic reproductions without the use of silver halides. The process uses salts of dichromate in common with a number of other related processes such as sun printing.

Architectural reprography, the reprography of architectural drawings, covers a variety of technologies, media, and supports typically used to make multiple copies of original technical drawings and related records created by architects, landscape architects, engineers, surveyors, mapmakers and other professionals in building and engineering trades.

Photographic film is a strip or sheet of transparent film base coated on one side with a gelatin emulsion containing microscopically small light-sensitive silver halide crystals. The sizes and other characteristics of the crystals determine the sensitivity, contrast, and resolution of the film. Film is typically segmented in frames, that give rise to separate photographs.

A heliographic copier or heliographic duplicator is an apparatus used in the world of reprography for making contact prints on paper from original drawings made with that purpose on tracing paper, parchment paper or any other transparent or translucent material using different procedures. In general terms some type of heliographic copier is used for making: Hectographic prints, Ferrogallic prints, Gel-lithographs or Silver halide prints. All of them, until a certain size, can be achieved using a contact printer with an appropriate lamp but for big engineering and architectural plans, the heliographic copiers used with the cyanotype and the diazotype technologies, are of the roller type, which makes them completely different from contact printers.

A photolith film is a transparent film, made with some sort of transparent plastic. Nowadays, with the use of laser printers and computers, the photolith film can be based on polyester, vegetable paper or laser film paper. It is mainly used in all photolithography processes.

A thermal copier or thermocopier is a kind of photocopier based on the effect of heat. The original sheet feeds in conjunction with the "thermo-sensitive" paper, generating a copy on its specially treated surface. The black parts on the original sheet, once scanned, make the copier activate the heating elements that produce some chemical reactions on the "thermo-sensitive" copy paper that darkens its surface. After the process, a stable black-and-white image is obtained on the cooled film or paper.

References

1 2 Cryder, George R. (November 1948). "Contact". Popular Mechanics. Hearst Magazines. pp. 216–. ISSN 0032-4558.
↑ Eva Zeisel; Robert Sabella (2006). Blueprints replaced by whiteprints. Que Certification. pp. 244–. ISBN 978-0-7897-3504-1.
↑ NIIR board (1 October 2002). Hand Book on Printing Technology (offset, Gravure, Flexo, Screen). National Institute Of Industrial Research. pp. 222–. ISBN 978-81-7833-087-7.

External links

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[Magazines1948-1] 1 2 Cryder, George R. (November 1948). "Contact". Popular Mechanics. Hearst Magazines. pp. 216–. ISSN 0032-4558.

[BlueprinReplaced2006-2] Eva Zeisel; Robert Sabella (2006). Blueprints replaced by whiteprints. Que Certification. pp. 244–. ISBN 978-0-7897-3504-1.

[Board2002-3] NIIR board (1 October 2002). Hand Book on Printing Technology (offset, Gravure, Flexo, Screen). National Institute Of Industrial Research. pp. 222–. ISBN 978-81-7833-087-7.

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