Shine a UV flashlight on a pale yellow-green glass bowl in an antique shop and it may erupt in blinding neon green. That is uranium glass, made by mixing uranium oxide into the batch before melting, and hundreds of thousands of pieces sit in cupboards today. This episode explains the chemistry of the glow, how excited electrons drop back to their resting state and emit green photons, and why most antique pieces contain one to two percent uranium while some 20th-century examples reached 25 percent by weight.

It traces a history that runs from yellow mosaic tiles in a Roman villa dated to 79 AD, through Bohemian silver miners discarding pitchblende, Martin Heinrich Klaproth’s isolation of uranium in 1789, and Franz Xaver Riedel’s Annagelb and Annagrün colors named for his daughter. It follows the golden age from the 1880s to the 1920s, Depression-era microcrystallization and iron oxide that produced Vaseline glass, jadeite and custard glass, the 1942 wartime confiscation of uranium supplies, and the graded seals still used in scientific vacuum equipment.

• Why the term Vaseline glass sparks arguments among collectors in different countries
• How adding fluorides and reheating turned transparent glass opaque
• Why US production ceased entirely from 1942 to 1958
• How uranium glass bridges Kovar metal and borosilicate glass in lab equipment
• What studies say about the actual radiation risk of eating off these plates