Sea glass glows because, in some cases, it contains uranium dioxide.
The Presence of Uranium Dioxide
Some sea glass, particularly pieces manufactured from the mid-1800s up until World War II, was made with uranium dioxide added to the glass mixture. This uranium dioxide causes the sea glass to fluoresce under ultraviolet (UV) light, such as that from a black light. This type of glass is often referred to as "uranium glass" or "UV glass."
Fluorescence Explained
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. In the case of uranium glass, the uranium dioxide absorbs the UV light and re-emits it as visible light, typically a bright yellow-green glow.
Examples of Uranium Glass
Uranium glass was commonly used to create various household items, including tableware. If you find a piece of sea glass with a yellow-green hue that glows under a black light, it's highly likely that it's uranium glass.
In summary, sea glass glows when it contains uranium dioxide, which fluoresces under ultraviolet light, emitting a visible yellow-green glow.
