Metal oxides associated with colors

Table I. Metal Oxides Associated with Colors of Medieval Glasses...

Cobalt ores are often found in association with copper(II) sulfide. Cobalt is a silver-gray metal and is used mainly for alloying with iron. Alnico steel, an alloy of iron, nickel, cobalt, and aluminum, is used to make permanent magnets such as those in loudspeakers. Cobalt steels are hard enough to be used as surgical steels, drill bits, and lathe tools. The color of cobalt glass is due to a blue pigment that forms when cobalt(II) oxide is heated with silica and alumina. 

Type B oxides have a metal excess which is incorporated into the lattice in interstitial positions. This is shown in (b)(1) as an interstitial atom, but it is more likely that the situation in (b)(ii) will hold, where the interstitial atom has ionised and the two electrons so released are now associated with two neighbouring ions, reducing them from to M. Cadmium oxide, CdO, has this type of structure. Oxygen is lost when zinc(II) oxide is heated, forming Zn +JD, oxide vacancies form and to compensate, Zn ions migrate to interstitial positions and are reduced to Zn ions or Zn atoms. Electron transfer can take place between the Zn and ZnTZn resulting in the yellow coloration seen when ZnO is heated. 

In another interesting amplification system, an image in silver or other noble metal nuclei is used for catalysis, and a cobalt(III) complex is used as an oxidant in place of a peroxy compound. The amplification permits less silver to be used. An imagewise distribution of silver nuclei is associated with a non-diffusible dye-forming coupler, and the image is amplified by (1) imbibing the system with a solution containing a color developer such as a p-phenylenediamine and (2)... 

THE glorious medieval stained-glass windows of European cathedrals have been the subject of several chemical analyses to support conservation projects, to identify workshops and their practices, and to attempt the association of colors with specific metal ions in various oxidation states. However, little information of this sort has been generated from the beautifully decorated, enameled, and gilded copper ecclesiastical objects used in medieval cathedrals that are recognized under the generic name of Limoges enamels. 

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