Dichromated

Dichromated is an adjective used in chemistry and materials science to describe a substance that contains dichromate, the dianion Cr2O7^2−, or that has been treated with a dichromate reagent. The most familiar dichromate species are the salts sodium dichromate, potassium dichromate, and ammonium dichromate, which are orange‑red crystalline solids and strong oxidizers. In aqueous solution, the relative amounts of dichromate and chromate depend on pH: dichromate predominates under acidic conditions, while chromate becomes more prevalent in basic solutions.

In photography, printing, and related fields, dichromated gelatin (DCG) is a historically important photosensitive system. Gelatin is sensitized with a dichromate salt and, upon exposure to ultraviolet or blue light, the exposed areas crosslink and become insoluble. Development with water removes the unexposed gelatin, leaving a relief image. DCG has been used to produce relief plates for letterpress printing, holographic recordings, and various microfabrication and lithographic applications.

Safety and handling considerations are important with dichromate compounds. They are toxic and carcinogenic, particularly when in hexavalent chromium form. Proper ventilation, personal protective equipment, and adherence to hazardous waste disposal regulations are required in both laboratory and industrial settings.

See also: chromate, chromium(VI) chemistry, dichromate salts, dichromated gelatin.