Allgemeine Therapie

Kempf,; Ostertag,; Hempel, Erich

doi:10.1007/bf01620347

Cited by 2 publications

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“…In addition, the silver bromide grains used in these investigations had several times the size of even the largest grains found in commercial emulsions, and had been prepared in the presence of inert gelatin. The same material was used by Kempf (52), who investigated the distribution of development centers at a single exposure level. The centers were found to be more numerous in the interior than at the surface.…”

Section: Distribution Of Development Centersmentioning

confidence: 99%

Reduction of Silver Halides and the Mechanism of Photographic Development.

James¹,

Kornfeld²

1942

Chem. Rev.

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Section: Distribution Of Development Centersmentioning

confidence: 99%

Reduction of Silver Halides and the Mechanism of Photographic Development.

James¹,

Kornfeld²

1942

Chem. Rev.

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“…There are at least two well-defined loss processes that interfere with this chemical reduction of silver ions: recombination of photoelectrons with photoholes, and reoxidation of silver atoms upon attack by photoholes. In a practical sense, the topography (location) of latent-image center formation on or within the microcrystal can also influence the effectiveness of the latent-image center as a catalytic site for subsequent amplification during development (7,(168)(169)(170). Chemical sensitizers increase the light sensitivity of the microcrystalline grains by separating photoholes from photoelectrons and from the site of latent-image formation.…”

Section: Chemical Sensitizationmentioning

confidence: 99%

Photography

Locker¹

2000

Kirk-Othmer Encyclopedia of Chemical Technology

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PHOTOGRAPHYThe unique light-sensing properties of silver halide crystals have been recognized since the 1500s. In spite of many technical advances in nonsilver halide (eg, electronic) technologies, chemically based silver halide systems continue to dominate in the ability to record images (1-3) of superb image quality and archival characteristics. Photochemical reduction in which the silver ion, Ag + , in the ionic silver halide crystal is reduced to elemental silver, Ag 0 (4-7) was first observed by the alchemist Fabricius in 1556. As photochemical reduction continues, elemental silver atoms aggregate and grow into clusters of a colloidal size sufficient to scatter light and produce hue shifts. The science of photography uses this photochemical property of silver halide to form images and record scenes. One of the earliest researchers to produce such a photochemical image was Schultze in 1727 (8). In these experiments, solutions of silver nitrate and white chalk were photochemically reduced to produce metallic silver images when the solutions were exposed through stencils.The daguerreotype process, prepared by Daguerre in 1837, and the calotype process, produced by Talbot in 1841, were among the first photographic techniques to produce continuous-tone images as reproductions of scenes (9, 10). The steps of a typical daguerreotype process include polishing and cleaning a silver-plated copper plate; treating the silver side of the plate with iodine vapors to convert silver into light-sensitive silver iodide [7783-96-2], AgI; exposing the plate through the optics of a camera that projects and focuses a scene on the plate, ie, where light strikes these plates, silver ions are photochemically reduced to silver metal; and treating the exposed plate with mercury. The mercury reacts with silver metal to produce a silver amalgam.White silver amalgam appears in areas of the plate exposed by light; the unexposed areas remain dark, thereby producing a positive image.Daguerrotype images were produced primarily by the action of light. For the production of satisfactory images, long exposures to light, on the order of minutes, were required because many absorbed photons were necessary to reduce photochemically enough silver ions to silver metal for visible imaging. In 1841, Talbot announced the calotype process, which could reduce exposure times to seconds and produce visible images without dependence on the action of light (11). In the calotype process, the exposure of silver halide produced an invisible latent image that was composed of only trace amounts of reduced silver. This acted as a catalyst for subsequent chemical reduction, ie, a nonphotochemical continuation of the light-initiated reduction process that eventually produced a visible silver image. In addition to being sensitive to much lower light levels, the calotype process was less expensive than the daguerreotype process and provided a negative-positive system that could generate several positive copies from a single negative original. The use of chemical amplif...

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Allgemeine Therapie

Cited by 2 publications

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Reduction of Silver Halides and the Mechanism of Photographic Development.

Reduction of Silver Halides and the Mechanism of Photographic Development.

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