There are a variety of examples of fluorescent substances. Emeralds, rubies, and Hope Diamonds give off red fluorescence under the presence of short-wave UV light. Petroleum can fluoresce in a wide array of colors, from brown for heavy oils to yellow and bluish white for light oils. Organic liquids of anthracene in toluene, stilbene, or benzene fluoresce with UV or gamma ray radiation. Rhodamine B is another example, and is a chemical compound that radiates light energy when mixed with water. A fluorescent lamp is an artificial source of light that uses fluorescence to emit light. It consists of argon and a small amount of mercury vapor in its structure.