During the first half of the 19th century, many photosensitive metal salts had been identified as candidates for photographic processes, among them uranyl nitrate. The prints thus produced were called uranium prints, urbanities, or more commonly, uranotypes. The first uranium printing processes were invented by Scotsman J. Charles Burnett between 1855 and 1857, and used this compound as the sensitive salt. Burnett authored a 1858article comparing "Printing by the Salts of the Uranic and Ferric Oxides" The process employs the ability of the uranyl ion to pick up two electrons and reduce to the lower oxidation state of uranium under ultraviolet light. Uranotypes can vary from print to print from a more neutral, brown russet to strong Bartolozzi red, with a very long tone grade. Surviving prints are slightly radioactive, a property which serves as a means of non-destructively identifying them. Several other more elaborate photographic processes employing the compound appeared and vanished during the second half of the 19th century with names like Wothlytype, Mercuro-Uranotype and the Auro-Uranium process. Uranium papers were manufactured commercially at least until the end of the 19th century, vanishing due to the superior sensitivity and practical advantages of silver halides. From the 1930s through the 1950s Kodak Books described a uranium toner using uranium nitrate hexahydrate. Some alternative process photographers including Blake Ferris and Robert Schramm continue to make uranotype prints today. Along with uranyl acetate it is used as a negative stain for viruses in electron microscopy; in tissue samples it stabilizes nucleic acids and cell membranes. Uranyl nitrate was used to fuel Aqueous Homogeneous Reactors in the 1950s as an alternative to the more corrosive uranyl sulfate. However, research focus was on heterogeneous reactor designs and the experiments were abandoned. Uranyl nitrate is important for nuclear reprocessing. It is the compound of uranium that results from dissolving the decladded spent nuclear fuel rods or yellowcake in nitric acid, for further separation and preparation of uranium hexafluoride for isotope separation for preparing of enriched uranium.
