Selenium glass is prized for its ability to produce warm colors ranging from soft pink to a deep, brilliant ruby red. It is an additive used in glassmaking to achieve these vibrant hues. Modern selenium glass is not considered radioactive and poses no health risk to users or collectors. Its coloration comes from a non-radioactive process that is entirely safe.
What Defines Selenium Glass
Selenium glass is created by adding the element selenium into the glass mixture during manufacturing. This element is typically introduced as sodium selenite or as part of cadmium sulfoselenide, depending on the desired color intensity. The concentration and firing temperature dictate the final shade, which can range from a delicate rose pink to a rich, opaque scarlet often referred to as “Selenium Ruby.”
Selenium is also used in small amounts to act as a de-colorizer. Glass often contains trace amounts of iron impurities, which create an undesirable greenish tint in clear glass. Adding selenium introduces a complementary pink hue that effectively neutralizes the green, resulting in a clearer, neutral-toned glass. This material is used in household glassware, decorative items, and industrial signal lenses.
The Direct Answer: Isotopic Stability
The safety of selenium glass lies in the element used in its manufacture. The selenium used in glass is composed of naturally occurring isotopes, the vast majority of which are stable.
The element selenium has six naturally occurring isotopes: Se-74, Se-76, Se-77, Se-78, Se-80, and Se-82. Five of these are completely stable, meaning their atomic nuclei do not decay over time. While selenium does possess unstable, or radioactive, isotopes, these forms are not used in commercial glass production.
One naturally occurring isotope, Selenium-82, is technically unstable but has an enormously long half-life of approximately 8.76 x 10^19 years. This decay rate is so slow that it is considered stable for all practical purposes, meaning it does not emit any measurable or harmful radiation. The selenium incorporated into glass does not undergo radioactive decay that releases harmful particles or energy.
Addressing the Confusion with Other Colored Glass
Confusion about selenium glass’s radioactivity often arises because it fluoresces under ultraviolet (UV) light. Selenium glass is known to glow a vibrant pink or orange under a blacklight, a property called fluorescence. This light-up effect often leads people to mistakenly believe the material is radioactive.
Uranium glass, commonly known as Vaseline glass, is genuinely radioactive. It achieves its signature yellow-green color and brilliant green fluorescence due to the addition of uranium compounds, which are naturally radioactive emitters. The uranium causes the glass to register above background radiation on a sensitive Geiger counter.
Selenium glass, in contrast, fluoresces due to the electron excitation caused by the UV light, not due to radioactive decay. The fluorescence of selenium glass is purely an optical effect. Other elements, such as manganese, can also be added to glass to create a purple tint and may also fluoresce under UV light, demonstrating that a glow does not automatically signal radioactivity.