Photography

Abstract

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...

The shear viscosity of polyampholyte (gelatin) stabilized colloidal dispersions

“…The colloidal stability imparted by polyampholytes through steric stabilization is of fundamental importance in industries ranging from photography to pharmaceuticals [1,2]. The adsorption of polyampholytes on colloidal surfaces provides stability and affects the thermodynamic properties and flow behavior of these suspensions [3].…”

Competitive Adsorption of Gelatin and Sodium Dodecylbenzenesulfonate at Hydrophobic Surfaces

“…Gelatin is a proteinaceous macromolecule derived from collagen, which is used extensively as a key component in photographic film together with silver halide crystallites, surfactants, dispersed oil droplets containing colorgenerating substances, and sensitizers. 1 Apart from film formation and viscocity control, gelatin plays a role in the stabilization of the crystallites and emulsion droplets in these applications. Since the performance of gelatin as a steric stabilizer in these mixed systems depends on the structure and composition of the adsorbed layer, there is a need for better understanding of the interfacial behavior of gelatin in mixed systems, particularly in the presence of surfactants.…”

“…Gelatin is a proteinaceous macromolecule derived from collagen, which is used extensively as a key component in photographic film together with silver halide crystallites, surfactants, dispersed oil droplets containing color-generating substances, and sensitizers . Apart from film formation and viscocity control, gelatin plays a role in the stabilization of the crystallites and emulsion droplets in these applications.…”

Sub-micron scale patterning of fluorescent silver nanoclusters using low-power laser

“…For example, synthetic polymers, DNA, dendrimer and some small molecules containing thiols and carboxylic groups can act as the stabilizing scaffold 1 2 3 4 . There is an abundance of literature about light-induced formation of silver nanoclusters using traditional photographic processes, where light reduces the silver ions into unstabilized silver clusters 13 14 and larger particles that are non-fluorescent. Similar to these processes, stabilized silver nanoclusters have been formed by direct laser writing (DLW) to create various fluorescent 2D and 3D structures 15 16 17 18 .…”