Photographic paper is paper coated with light-sensitive chemicals, used for making photographic prints. Photographic paper differs from photo papers: specially coated papers for use in inkjet or laser printers to make digital prints.

Photographic paper is exposed to light in a controlled manner, either by placing a negative in contact with the paper directly to produce a contact print, by using an enlarger in order to create a latent image, by exposing in some types of camera to produce a photographic negative, or by placing objects upon it to produce photograms. Photographic papers are subsequently developed using the gelatin-silver process to create a visible image.

History

The effect of light in darkening a prepared paper was discovered by M. Charles in 1800 or by Thomas Wedgwood in 1802.^[1]

Photographic papers have been used since the beginning of all negative?positive photographic processes as developed and popularised by William Fox Talbot (Great Britain/1841-calotype).

Traditional photographic papers are still sold commercially today.

Types of photographic papers

Photographic papers fall into one of three sub-catergories:

Papers used for negative-positive processes. This includes all current black and white papers and chromogenic colour papers.

Papers used for positive-positive processes in which the "film" is the same as the final image (e.g. the Polaroid process).

Papers used for positive-positive film-to-paper processes where a positive image is enlarged and copied onto a photographic paper, for example the Ilfochrome process.

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 sensitised to blue and green light to facilitate handling under red/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.

Fibre-based papers (FB)

Fibre-based (FB or Baryta) photographic papers consist of a paper base coated with a baryta. 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 fibre-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 supercoating are suitable for use with the bromoil process. ^[2]

Fibre-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 photographic papers is sealed against the chemicals used for processing the paper by two polyethylene layers. Since no chemicals and no water is soaked into the paper base the time needed for processing, washing and drying of the paper is significantly shorter than the time needed for fibre-based papers. Resin paper prints can be finished and dried within ten to fifteen minutes. All current colour papers are coated onto a resin or polyester base.

Most resin-coated photographic papers are also supercoated.

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 color 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".

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 color films.

The emulsion layers include the colour dyes (Ilfochrome) or "colour couplers" which react with colour developers to produce colour dyes (Type C prints). "Type C" is a trademark of Eastman Kodak which has been applied generically to other negative-positive print system. Common usage has made this trademark universal. More accurately, these are Chromogenic negative-positive prints. The so called Type R prints which are no longer made, were also misusage of a Kodak trademark. These products were more properly called pos-pos chromogenic prints.

Emulsion characteristics

The emulsion itself is made up from light sensitive silver halide crystals suspended in gelatin.

Photographic papers are distinguished by the characteristics inherent in their different photographic emulsions. Black-and-white photographic paper is available in different grades which are usually numbered 0 to 5, with 0 being the softest, or least contrastful paper grade and 5 being the hardest, or most contrastful paper grade.

Photographic emulsions are also produced in a variable contrast type which permits the selection of any grade between 00 and 5. Variable contrast photographic paper is actually coated with a mixture of two types of emulsion, one of which is very low in contrast (0 or 00) and one of which is very high in contrast (5). The low contrast layer is activated by green light, the high contrast layer by blue light. The use of filters activates each layer in different proportions, thereby creating all contrast grades from 0 (or 00) to 5.

The trade names of variable contrast photographic papers typically include a reference to contrast variability, such as Variocontrast, Multigrade, Varycon or similar. Some companies simply designate variable contrast type papers with the words variable or polycontrast.

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

Archival stability

The actual life span of any given photographic paper will vary with the environment the paper is stored within and how well the paper was processed.

Fibre-based black-and-white photographic paper that has been processed archivally (i.e. has been fixed and watered properly) is considered archivally "stable" and should last at least 70 years (the life-span of a typical resin-coated print is usually around 30-40 years.) Some special processes include photographic emulsions that are, if processed correctly, inherently more stable than the paper base they are printed upon, such as platinum prints.

Standard print sizes

Standard photographic print sizes are often denoted with a code of the format nR, where the number n represents the length of the shorter edge in inches. In the normal series, the long edge is the length of the short edge plus 2 inches (10" or less) or 3 inches (11" and above). The alternative Super series, denoted SnR has an aspect ratio of 3:2 (or as close as possible) and thus provides a better fit for standard 135 film (35mm) at sizes of 8 inches or above.

In Japan, the same print sizes (and several additional ones) are known by different names. The Japanese L is equivalent to 3R, while 2L — twice the size — matches 5R. KG represents the size of a traditional 4"×6" (4R) Japanese postcard (hagaki).^[4] The nP or series are defined in reference to a of 457×560 mm, with smaller numbers (fewer cuts) indicating larger sizes.^[5]

Unlike ISO 216 paper sizes, the aspect ratios of photographic prints vary, so exact scaling of prints is not always possible. However, there are some logical correspondences between the sizes, noted below when applicable.

See also

• Film base
• Photographic print toning
• Inkjet paper
• Photographic printing
• Cutting stock problem

References

1. ↑
2. ↑ ^{a b}
3. ↑ ^{a b}
4. ↑ ????????????????????????? -?????????PAM
5. ↑ Traditional Japanese Specialty Papers
6. ↑ At 368mm, the Japanese 4PW size is slightly narrower than S10R.

External links

Manufacturers of B/W Photographic Papers

• Ilford Photo, UK
• Kentmere, UK
• Fotokemika, Croatia
• Fuji, Japan
• Foma, Czech Republic
• Slavich, Russia

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