Silver compounds physical development

Latent images or faint images in silver metal or other materials can be amplified by redox chemistries other than metal deposition. Several dye-forming redox chemistries have been discovered in which metal complexes serve as catalysts, catalyst precursors or one of the redox partners. The applications of coordination compounds in physical development and image amplification systems are therefore quite broad and diverse. 

Silver halide grains are used as the light-sensitive component in many solution processes involving physical development. The latent images or partially developed latent images comprise the nuclei upon which the physical development reactions are catalyzed. There are many other nuclei-forming compounds, however, which find use in systems where the speed of silver halide is not required, its expense is unsuitable, or a more efficient catalyst for the physical development reaction is desired. 

Silver and silver-copper alloys are often even more sensitive to sulfur compounds—the effect is catalyzed in the presence of oxidizing species and high relative humidity [268]. The resulting surface layer—dark, thin and adherent when developed on a polished surface—usually acts as a good physical barrier that slows down the tarnishing reactions. However, since silver objects are expected to be shiny. 

Although the elements, gold (Au), silver (Ag), tin (Sn), copper (Cu), lead (Pb), mercury (Hg), antimony (Sb), arsenic (As), carbon (C), iron (Fe), sulfur (S) and zinc (Zn) had been known since ancient times, the first scientific discovery of an element occurred in 1669, when Hennig Brand discovered phosphorus (P). During the next two hundred years various chemical and physical properties of elements and their compounds were studied by chemists. By 1869, a total of 63 elements had been discovered. As the number of known elements increased, scientists began to recognize patterns in properties and began to develop classification schemes. 

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