Uranotype photograph.
An example of the element Uranium

In the 19th century, when silver-based photography was just one approach among many others, UV-sensitive uranium salts were a familiar part of the early photographer's formulary. Commercial uranium printing paper was manufactured until 1899, and mixtures containing uranyl nitrate were commonly used to tone and intensify silver prints well into the 20th century. In earlier times, the uranyl compounds were made from undepleted uranium, and had non-negligible gamma emissions. Today, uranium photography is virtually nonexistent, but Kodak still makes a uranium toner, and uranyl acetate is regularly used in electron microscopy.

Many printing processes using uranium, together with other metal salts, were referred to as "uranotypes", but the picture here (the Nagasaki explosion, negative from the U.S. National Archives) is a true uranotype, insofar as the image is formed after development by the orange pigment uranyl ferricyanide (in most other uranium processes, the uranium would form an oxide and wash out after reducing another metal salt). The process gives a low-contrast image resembling a "red chalk" drawing, and results in a print that registers about 200 cpm above background after washing and drying.