Vaseline glass glows neon green under UV light because it contains uranium.

Vaseline glass, also known as uranium glass, typically contains between 0.1% and 2% uranium dioxide by weight. This additive was first popularized by Josef Reidel in Bohemia during the 1830s to create vibrant yellow and green hues. The characteristic glow is a result of fluorescence, where ultraviolet radiation excites the electrons in the uranium atoms. As these electrons return to their ground state, they release energy in the form of visible green light.The radioactivity of these pieces is generally considered negligible for collectors. According to the U.S. Nuclear Regulatory Commission, the radiation dose from a piece of uranium glass is often less than the background radiation a person receives from natural sources like soil and stone. Most pieces emit about 0.1 to 2 millirems per hour, which is well below the threshold for health concerns when handled normally.The production of uranium glass faced a major disruption in 1943 during World War II. The United States government seized all uranium supplies for the Manhattan Project to develop the first atomic bombs. While production resumed in 1958 using depleted uranium, the original 'Vaseline' glass from the Victorian and Depression eras remains the most sought after by enthusiasts. Modern collectors use 365nm or 395nm UV flashlights to verify the authenticity of these historical items.