Photographic paper

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Photographic paper is a paper coated with a light-sensitive chemical formula, like photographic film, used for making photographic prints. When photographic paper is exposed to light, it captures a latent image that is then developed to form a visible image; with most papers the image density from exposure can be sufficient to not require further development, aside from fixing and clearing, though latent exposure is also usually present. The light-sensitive layer of the paper is called the emulsion. The most common chemistry was based on silver halide (the focus of this page) but other alternatives have also been used.

Contents

The print image is traditionally produced by interposing a photographic negative between the light source and the paper, either by direct contact with a large negative (forming a contact print) or by projecting the shadow of the negative onto the paper (producing an enlargement). The initial light exposure is carefully controlled to produce a gray scale image on the paper with appropriate contrast and gradation. Photographic paper may also be exposed to light using digital printers such as the LightJet, with a camera (to produce a photographic negative), by scanning a modulated light source over the paper, or by placing objects upon it (to produce a photogram).

Despite the introduction of digital photography, photographic papers are still sold commercially. Photographic papers are manufactured in numerous standard sizes, paper weights and surface finishes. A range of emulsions are also available that differ in their light sensitivity, colour response and the warmth of the final image. Color papers are also available for making colour images.

History

The effect of light in darkening a prepared paper was discovered by Thomas Wedgwood in 1802. [1] Photographic papers have been used since the beginning of all negative–positive photographic processes as developed and popularized by William Fox Talbot (Great Britain/1841-calotype).

After the early days of photography, papers have been manufactured on a large scale with improved consistency and greater light sensitivity.

Types of photographic papers

Types of Photographic Papers.png

Photographic papers fall into one of three sub-categories:

Structure

All photographic papers consist of a light-sensitive emulsion, consisting of silver halide salts suspended in a colloidal material – usually gelatin-coated onto a paper, resin coated paper or polyester support. In black-and-white papers, the emulsion is normally sensitised to blue and green light, but is insensitive to wavelengths longer than 600 nm in order to facilitate handling under red or orange safelighting. [2] In chromogenic colour papers, the emulsion layers are sensitive to red, green and blue light, respectively producing cyan, magenta and yellow dye during processing.

Base materials

Black-and-white papers

Modern black-and-white papers are coated on a small range of bases; baryta-coated paper, resin-coated paper or polyester. In the past, linen has been used as a base material. [3]

Fiber-based papers (FB)

Fiber-based (FB or Baryta) photographic papers consist of a paper base coated with baryta. [4] Tints are sometimes added to the baryta to add subtle colour to the final print; however most modern papers use optical brighteners to extend the paper's tonal range. [3] Most fiber-based papers include a clear hardened gelatin layer above the emulsion which protects it from physical damage, especially during processing. This is called a supercoating. Papers without a super coating are suitable for use with the bromoil process. [2] Fiber-based papers are generally chosen as a medium for high-quality prints for exhibition, display and archiving purposes. These papers require careful processing and handling, especially when wet. However, they are easier to tone, hand-colour and retouch than resin-coated equivalents. [3]

Resin-coated papers (RC)

The paper base of resin-coated papers is sealed by two polyethylene layers, making it impenetrable to liquids. Since no chemicals or water are absorbed into the paper base, the time needed for processing, washing and drying durations are significantly reduced in comparison to fiber-based papers. Resin paper prints can be finished and dried within twenty to thirty minutes. Resin-coated papers have improved dimensional stability, and do not curl upon drying. [3]

The baryta layer

The term baryta derives from the name of a common barium sulfate-containing mineral, barite. However, the substance used to coat photographic papers is usually not pure barium sulfate, but a mixture of barium and strontium sulfates. The ratio of strontium to barium differs among commercial photographic papers, so chemical analysis can be used to identify the maker of the paper used to make a print and sometimes when the paper was made. [5] The baryta layer has two functions 1) to brighten the image and 2) to prevent chemicals adsorbed on the fibers from infiltrating the gelatin layer. The brightening occurs because barium sulfate is in the form of a fine precipitate that scatters light back through the silver image layer. In the early days of photography, before baryta layers were used, impurities from the paper fibers could gradually diffuse into the silver layer and cause an uneven loss of sensitivity (before development) or mottle (unevenly discolour) the silver image (after development). [4]

Colour papers

All colour photographic materials available today are coated on either RC (resin coated) paper or on solid polyester. The photographic emulsion used for colour photographic materials consists of three colour emulsion layers (cyan, yellow, and magenta) along with other supporting layers. The colour layers are sensitised to their corresponding colours. Although it is commonly believed that the layers in negative papers are shielded against the intrusion of light of a different wavelength than the actual layer by colour filters which dissolve during processing, this is not so. The colour layers in negative papers are actually produced to have speeds which increase from cyan (red sensitive) to magenta (green sensitive) to yellow (blue sensitive), and thus when filtered during printing, the blue light is "normalized" so that there is no crosstalk. Therefore, the yellow (blue sensitive) layer is nearly ISO 100 while the cyan (red) layer is about ISO 25. After adding enough yellow filtration to make a neutral, the blue sensitivity of the slow cyan layer is "lost". [ citation needed ]

In negative-positive print systems, the blue sensitive layer is on the bottom, and the cyan layer is on the top. This is the reverse of the usual layer order in colour films. [6]

The emulsion layers can include the colour dyes, as in Ilfochrome; or they can include colour couplers, which react with colour developers to produce colour dyes, as in type C prints or chromogenic negative–positive prints. Type R prints, which are no longer made, were positive–positive chromogenic prints. [7]

Black and white emulsion types

The emulsion contains light sensitive silver halide crystals suspended in gelatin. Black-and-white papers typically use relatively insensitive emulsions composed of agb silver bromide, silver chloride or a combination of both. The silver halide used affects the paper's sensitivity and the image tone of the resulting print. [2]

Chloride papers

Popular in the past, chloride papers are nowadays unusual; a single manufacturer produces this material. [8] These insensitive papers are suitable for contact printing, and yield warm toned images by development. Chloride emulsions are also used for printing-out papers, or POP, which require no further development after exposure. [9] [10]

Chlorobromide papers

Containing a blend of silver chloride and silver bromide salts, these emulsions produce papers sensitive enough to be used for enlarging. They produce warm-black to neutral image tones by development, which can be varied by using different developers. [3]

Bromide papers

Papers with pure silver bromide emulsions are sensitive and produce neutral black or 'cold' blue-black image tones. [2]

Contrast control

Fixed-grade – or graded – black-and-white papers were historically available in a range of 12 grades, numbered 0 to 5, with 0 being the softest, or least contrasty paper grade and 5 being the hardest, or most contrasty paper grade. Low contrast negatives can be corrected by printing on a contrasty paper; conversely a very contrasty negative can be printed on a low contrast paper. [2] Because of decreased demand, most extreme paper grades are now discontinued, and the few graded ranges still available include only middle contrast grades. [10]

Variable-contrast – or "VC" – papers account for the great majority of consumption of these papers in the 21st century. VC papers permit the selection of a wide range of contrast grades, in the case of the brand leader between 00 and 5. These papers are coated with a mixture of two or three emulsions, all of equal contrast and sensitivity to blue light. However, each emulsion is sensitised in different proportions to green light. Upon exposure to blue light, all emulsions act in an additive manner to produce a high contrast image. When exposed to green light alone, the emulsions produce a low contrast image because each is differently sensitised to green. By varying the ratio of blue to green light, the contrast of the print can be approximately continuously varied between these extremes, creating all contrast grades from 00 to 5. [11] Filters in the enlarger's light path are a common method of achieving this control. Magenta filters absorb green and transmit blue and red, while yellow filters absorb blue and transmit green and red. [12]

The contrast of photographic papers can also be controlled during processing or by the use of bleaches or toners.[ citation needed ]

Panchromatic papers

Panchromatic black-and-white photographic printing papers are sensitive to all wavelengths of visible light. They were designed for the printing of full-tone black-and-white images from colour negatives; this is not possible with conventional orthochromatic papers. Panchromatic papers can also be used to produce paper negatives in large-format cameras. These materials must be handled and developed in near-complete darkness. Kodak Panalure Select RC is an example of a panchromatic black-and-white paper; it was discontinued in 2005. [13]

Non Silver papers

Numerous photo sensitive papers that do not use silver chemistry exist. Most are hand made by enthusiasts but cyanotype prints are made on what was commonly sold as blueprint paper. Certain precious metal including platinum and other chemistries have also been in common use at certain periods.

Archival stability

The longevity of any photographic print media will depend upon the processing, display and storage conditions of the print.

Black-and-white prints

Fixing must convert all non-image silver into soluble silver compounds that can be removed by washing with water. Washing must remove these compounds and all residual fixing chemicals from the emulsion and paper base. A hypo-clearing solution, also referred to as hypo clearing agent, HCA, or a washing aid, and which can consist of a 2% solution of sodium sulfite, [14] can be used to shorten the effective washing time by displacing the thiosulfate fixer, and the byproducts of the process of fixation, that are bound to paper fibers. [15]

Toners are sometimes used to convert the metallic silver into more stable compounds. Commonly used archival toners are: selenium, gold and sulfide.

Prints on fiber-based papers that have been properly fixed and washed should last at least fifty years without fading. Some alternative non-silver processes – such as platinum prints – employ metals that are, if processed correctly, inherently more stable than gelatin-silver prints. [2]

Colour prints

For colour images, Ilfochrome is often used because of its clarity and the stability of the colour dyes.[ citation needed ]

See also

Related Research Articles

Film stock Medium used for recording motion pictures

Film stock is an analog medium that is used for recording motion pictures or animation. It is recorded on by a movie camera, developed, edited, and projected onto a screen using a movie projector. It is a strip or sheet of transparent plastic 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. The emulsion will gradually darken if left exposed to light, but the process is too slow and incomplete to be of any practical use. Instead, a very short exposure to the image formed by a camera lens is used to produce only a very slight chemical change, proportional to the amount of light absorbed by each crystal. This creates an invisible latent image in the emulsion, which can be chemically developed into a visible photograph. In addition to visible light, all films are sensitive to X-rays and high-energy particles. Most are at least slightly sensitive to invisible ultraviolet (UV) light. Some special-purpose films are sensitive into the infrared (IR) region of the spectrum.

Photographic developer

In the processing of photographic films, plates or papers, the photographic developer is one or more chemicals that convert the latent image to a visible image. Developing agents achieve this conversion by reducing the silver halides, which are pale-colored, into silver metal, which is black. The conversion occurs within the gelatine matrix. The special feature of photography is that the developer acts more quickly on those particles of silver halides that have been exposed to light. Paper left in developer will eventually reduce all the silver halides and turn black. Generally, the longer a developer is allowed to work, the darker the image.

Negative (photography) Image on photographic film

In photography, a negative is an image, usually on a strip or sheet of transparent plastic film, in which the lightest areas of the photographed subject appear darkest and the darkest areas appear lightest. This reversed order occurs because the extremely light-sensitive chemicals a camera film must use to capture an image quickly enough for ordinary picture-taking are darkened, rather than bleached, by exposure to light and subsequent photographic processing.

Albumen print Photographic process

The albumen print, also called albumen silver print, was published in January 1847 by Louis Désiré Blanquart-Evrard, and was the first commercially exploitable method of producing a photographic print on a paper base from a negative. It used the albumen found in egg whites to bind the photographic chemicals to the paper and 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 Photography that reproduces colors

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.

Gelatin silver process Photographic process

The gelatin silver process 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. This was an improvement on the collodion wet-plate process dominant from the 1850s–1880s, which had to be exposed and developed immediately after coating.

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".

C-41 is a chromogenic color print film developing process introduced by Kodak in 1972, superseding the C-22 process. C-41, also known as CN-16 by Fuji, CNK-4 by Konica, and AP-70 by AGFA, is the most popular film process in use, with most photofinishing labs devoting at least one machine to this development process.

Platinum print

Platinum prints, also called platinotypes, are photographic prints made by a monochrome printing process involving platinum.

Print permanence refers to the longevity of printed material, especially photographs, and preservation issues. Over time, the optical density, color balance, lustre, and other qualities of a print will degrade. The rate at which deterioration occurs depends primarily on two main factors: the print itself, that is, the colorants used to form the image and the medium on which image resides, and the type of environment the print is exposed to.

The conservation and restoration of photographs is the study of the physical care and treatment of photographic materials. It covers both efforts undertaken by photograph conservators, librarians, archivists, and museum curators who manage photograph collections at a variety of cultural heritage institutions, as well as steps taken to preserve collections of personal and family photographs. It is an umbrella term that includes both preventative preservation activities such as environmental control and conservation techniques that involve treating individual items. Both preservation and conservation require an in-depth understanding of how photographs are made, and the causes and prevention of deterioration. Conservator-restorers use this knowledge to treat photographic materials, stabilizing them from further deterioration, and sometimes restoring them for aesthetic purposes.

Chromogenic photography is photography that works by a chromogen forming a conventional silver image and then replacing it with a dye image. Most films and papers used for color photography today are chromogenic, using three layers, each providing their own subtractive color. Some chromogenic films provide black-and-white negatives, and are processed in standard color developers. In this case, the dyes are a neutral color.

A chromogenic print, also known as a C-print or C-type print, a silver halide print, or a dye coupler print, is a photographic print made from a color negative, transparency or digital image, and developed using a chromogenic process. They are composed of three layers of gelatin, each containing an emulsion of silver halide, which is used as a light-sensitive material, and a different dye coupler of subtractive color which together, when developed, form a full-color image.

Color motion picture film Photographic film type

Color motion picture film refers both to unexposed color photographic film in a format suitable for use in a motion picture camera, and to finished motion picture film, ready for use in a projector, which bears images in color.

Duplitized film was a type of motion picture print film stock used for some two-color natural color processes. It was introduced by Eastman Kodak around 1913. The stock was of standard gauge and thickness, but it had a photographic emulsion coated on both sides of the film base instead of on one surface only.

Photographic emulsion is a light-sensitive colloid used in film-based photography. Most commonly, in silver-gelatin photography, it consists of silver halide crystals dispersed in gelatin. The emulsion is usually coated onto a substrate of glass, films, paper, or fabric.

Dye transfer is a continuous-tone color photographic printing process. It was used to print Technicolor films, as well as to produce paper colour prints used in advertising, or large transparencies for display.

Photographic film Film used by film (analog) cameras

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.

Art photography print types refers to the process and paper of how the photograph is printed and developed.

A contact copier, is a device used to copy an image by illuminating a film negative with the image in direct contact with a photosensitive surface. 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 actínic bulb internal or external to the device

References

  1. ↑ Sydney Smith; Francis Jeffrey Jeffrey; Macvey Napier; William Empson; George Cornewall (1843), The Edinburgh Review, London: Longman, Orme, Brown, Green, and Longmans; and Edinburgh: Adam and Charles Black
  2. 1 2 3 4 5 6 Sowerby, A.L.M., ed. (1961), Dictionary of Photography: A Reference Book for Amateur and Professional Photographers (19th ed.), London: Illife Books Ltd.
  3. 1 2 3 4 5 Langford, Michell (2000), Basic Photography (7th ed.), Oxford, England.: Focal Press, ISBN   0-240-51592-7
  4. 1 2 Salvaggio, Nanette L. Basic Photographic Materials and Processes. Taylor & Francis US, Oct 27, 2008. p. 362.
  5. ↑ Everts, Sarah Saving endangered photographs. Chemical & Engineering News 25 Feb 2013, pp 9-14.
  6. ↑ http://www.fujifilmusa.com/shared/bin/AF3-155E_Fujitrans_PIB.pdf [ bare URL PDF ]
  7. ↑ Processing Kodak Ektachrome RC paper, type 1993 in Kodak rapid colour processors. Eastman Kodak Company. 1974. OCLC   43350075.
  8. ↑ Chamlee, Paula; Smith, Michael A. (2008), Lodima: Replacement Paper for Azo , retrieved 2008-10-03
  9. ↑ Anchell, Steve (February 26, 2011), Printing-Out Processes, archived from the original on March 2, 2016, retrieved 2016-02-18
  10. 1 2 Reed, Martin (1998), Yesterday's paper (published 2004), archived from the original on 2008-10-07, retrieved 2008-10-03
  11. ↑ THE WORKINGS OF VARIABLE CONTRAST PAPERS AND LOCAL GAMMA (PDF), retrieved 2013-07-17
  12. ↑ Ilford Imaging UK LTD. (April 2010), Contrast Control for Ilford Multigrade Variable Contrast Papers (PDF), retrieved 2018-10-01
  13. ↑ unknown (June 2005). "Kodak Professional Panalure Select RC Paper" (PDF). Eastman Kodak Company. Retrieved 14 March 2010.
  14. ↑ Anchell, Steve (2008). "Formulas". The Darkroom Cookbook (3rd ed.). Focal Press. p.  312. ISBN   978-0-240-81055-3.
  15. ↑ Kachel, David. Fixing, Washing & Toning Fine B&W Photographs: Processing Your Materials Correctly Archived 2012-04-18 at the Wayback Machine
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