luminosity

This brightly colored coffee cup is an example of uranium glass. Sometimes known as vaseline glass, depending on the color, uranium glass glows very brightly under long-wave ultraviolet lighting. A lot of this glass, part of the broader family known as depression glass, was manufactured in the Midwestern US between the 1920's and '40s. The addition of extremely minute amounts of uranium is what gives the glass its characteristic color in natural light; it's also what glows so very intensely under UV light.