In this Article we will discuss about Photographic Paper.Photographic paper is a Paper Coated with a light-sensitive chemical formula, 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. The light-sensitive layer of the paper is called the emulsion.
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 or by projecting the shadow of the negative onto the paper (producing an enlargement). The initial light exposure is carefully controlled to produce a grey 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 by scanning a modulated light source over the paper, or by placing objects upon it.
Despite the introduction of digital photography, photographic papers and 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, color response and the warmth of the final image. Color Papers are also available for making Color Images.
History
The effect of light in darkening a prepared paper was discovered by M. Charles in 1800 or by Thomas Wegdwoodin 1802. Photographic papers have been used since the beginning of all negative–positive.
After the early days of photography, papers have been manufactured on a large scale with improved consistency and greater light sensitivity.
Types of Photographic Paper
Photographic papers fall into one of three sub-categories:
- Papers used for negative-positive processes. This includes all current Black and white papers and chromogenic color papers.
- Papers used for positive-positive processes in which the "film" is the same as the final image
- Papers used for positive-positive film-to-paper processes where a positive image is enlarged and copied onto a photographic paper.
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 safelightning. In Chromogenic color papers, the emulsion layers are sensitive to red,green and blue light, respectively producing cyan,magenta and yellow dye during processing.
Base materials
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.
Fiber-based papers (FB)
Fiber-based (FB or Baryta) photographic papers consist of a paper base coated with baryta. Tints are sometimes added to the baryta to add subtle color to the final print; however most modern papers use optical brightners to extend the paper's tonal range. 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 supercoating are suitable for use with the bromoil process. 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-color and retouch than resin-coated equivalents.
Resin-coated papers (RC)
The paper base of resin-coated papers is sealed by two polyethene 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.
Color papers
All color photographic materials available today are coated on either RC (resin coated) paper or on solid polyester. The photographic emulsion used for color photographic materials consists of three color emulsion layers along with other supporting layers. The color layers are sensitised to their corresponding colors. 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 color 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 can include the color dyes, as in Ilfochrome; or they can include color couplers, which react with color developers to produce color dyes, as in type c prints or chromogenic negative–positive prints. Type R prints, which are no longer made, were positive–positive chromogenic prints.
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