Buried in the table of contents of a slim 1939 Soviet photography manual is a section heading that would make a modern darkroom hobbyist's eyebrows climb to their hairline:

Вирирование солями урана... Коричневый цвет... Темнокоричневый цвет... Красно-коричневый цвет.

That is: "Toning with uranium salts — brown color, dark brown color, red-brown color." A nine-page chapter of a state-published amateur photographer's handbook, casually instructing hobbyists on how to use uranium compounds to color their family snapshots.

The book is Volume 10 of the Библиотека фотолюбителя (Amateur Photographer's Library), published in Moscow by Goskinoizdat in 1939. Its author, В. Яштолд-Говорко (V. Yashtold-Govorko), was a prolific Soviet writer on photographic chemistry. The book is a methodical catalog of how to chemically replace the silver in a black-and-white print with metal salts to produce different colors: iron for blue, copper for red, cobalt for salad-green, lead for yellow, nickel for cherry-red — and uranium for a distinctive warm red-brown that no other toner could quite match.

The author opens with a perfectly sensible aesthetic argument:

"You cannot, for example, tint a portrait green or bright blue. This will only ruin the picture. At the same time, coloring a portrait in brown or red-brown tones can significantly improve its quality."

Uranium toning was genuinely common from the 1890s through the 1950s. The chemistry involved uranyl nitrate and potassium ferricyanide, which deposited uranium ferrocyanide in the image, producing a saturated red-brown that photographers prized for landscapes and autumn scenes. It was sold in commercial kits by Kodak and Agfa.

The forgotten part: those prints are mildly radioactive — and still are, sitting in family albums and museum archives across the world. Conservators today routinely identify uranium-toned prints by sweeping them with Geiger counters. The activity is low (depleted-uranium territory), but it's real and permanent. The half-life of uranium-238 is 4.5 billion years; your great-grandmother's sepia-toned photograph will outlast the sun.

What makes this so striking to a modern reader is the casualness. There is no warning. No protective-equipment note. Uranium is listed between cobalt and aniline dyes as just another option on the color palette, the way a modern art store might shelve cadmium-red watercolors. Nuclear fission had been demonstrated only months before this book went to press — Hahn and Strassmann's paper appeared in Naturwissenschaften in January 1939 — and Soviet hobbyists were being told how to handle uranyl nitrate in their kitchen sinks.

The technique vanished not because it stopped working, but because the regulatory landscape around uranium tightened dramatically after 1945. By the 1960s uranyl salts were nearly impossible for amateurs to buy. An entire visual aesthetic — the deep, glowing red-brown of a uranium-toned print — was effectively legislated out of existence.