Structure Photographic paper

1 structure

1.1 base materials

1.1.1 black-and-white papers

1.1.1.1 fiber-based papers (fb)
1.1.1.2 resin-coated papers (rc)
1.1.1.3 baryta layer


1.1.2 colour papers

structure

all photographic papers consist of light-sensitive emulsion, consisting of silver halide salts suspended in colloidal material - gelatin- coated onto paper, resin coated paper or polyester support. in black-and-white papers, emulsion sensitised blue , green light, insensitive wavelengths longer 600 nm in order facilitate handling under red or orange safelighting. in chromogenic colour papers, emulsion layers sensitive red, green , blue light, respectively producing cyan, magenta , yellow dye during processing.

base materials
black-and-white papers

modern black-and-white papers coated on small range of bases; baryta-coated paper, resin-coated paper or polyester. in past, linen has been used base material.

fiber-based papers (fb)

fiber-based (fb or baryta) photographic papers consist of paper base coated baryta. tints added baryta add subtle colour final print; modern papers use optical brighteners extend paper s tonal range. fiber-based papers include clear hardened gelatin layer above emulsion protects physical damage, during processing. called supercoating. papers without supercoating suitable use bromoil process. fiber-based papers chosen medium high-quality prints exhibition, display , archiving purposes. these papers require careful processing , handling, when wet. however, easier tone, hand-colour , retouch resin-coated equivalents.

resin-coated papers (rc)

the paper base of resin-coated papers sealed 2 polyethylene layers, making impenetrable liquids. since no chemicals or water absorbed paper base, time needed processing, washing , drying durations reduced in comparison fiber-based papers. resin paper prints can finished , dried within twenty thirty minutes. resin-coated papers have improved dimensional stability, , not curl upon drying.

the baryta layer

the term baryta derives name of common barium sulfate-containing mineral, barite. however, substance used coat photographic papers not pure barium sulfate, mixture of barium , strontium sulfates. ratio of strontium barium differs among commercial photographic papers, chemical analysis can used identify maker of paper used make print , when paper made. baryta layer has 2 functions 1) brighten image , 2) prevent chemicals adsorbed on fibers infiltrating gelatin layer. brightening occurs because barium sulfate in form of fine precipitate scatters light through silver image layer. in days of photography, before baryta layers used, impurities paper fibers gradually diffuse silver layer , cause uneven loss of sensitivity (before development) or mottle (unevenly discoluor) silver image (after development).

colour papers

all colour photographic materials available today coated on either rc (resin coated) paper or on solid polyester. photographic emulsion used colour photographic materials consists of 3 colour emulsion layers (cyan, yellow, , magenta) along other supporting layers. colour layers sensitised corresponding colours. although commonly believed layers in negative papers shielded against intrusion of light of different wavelength actual layer colour filters dissolve during processing, not so. colour layers in negative papers produced have speeds increase cyan (red sensitive) magenta (green sensitive) yellow (blue sensitive), , when filtered during printing, blue light normalized there no crosstalk. therefore, yellow (blue sensitive) layer iso 100 while cyan (red) layer iso 25. after adding enough yellow filtration make neutral, blue sensitivity of slow cyan layer lost .

in negative-positive print systems, blue sensitive layer on bottom, , cyan layer on top. reverse of usual layer order in colour films.

the emulsion layers can include colour dyes, in ilfochrome; or can include colour couplers, react colour developers produce colour dyes, in type c prints or chromogenic negative–positive prints. type r prints, no longer made, positive–positive chromogenic prints.