Bismuth is a chemical element with the symbol Bi and atomic number 83. It is a weakly radioactive post-transition metal and one of the pnictogens, with chemical properties resembling its lighter group 15 siblings arsenic and antimony. Elemental bismuth may occur naturally, and its sulfide and oxide forms are important commercial ores. The free element is 86% as dense as lead. It is a brittle metal with a silvery-white color when freshly produced. Surface oxidation generally gives samples of the metal a somewhat rosy cast. Further oxidation under heat can give bismuth a vividly iridescent appearance due to thin-film interference. Bismuth is both the most diamagnetic element and one of the least thermally conductive metals known. Bismuth was long considered the element with the highest atomic mass whose nuclei do not spontaneously decay. However, in 2003 it was discovered to be extremely weakly radioactive. The metals only primordial isotope, bismuth-209, experiences alpha decay at such a minute rate that its half-life is more than a billion times the estimated age of the observable universe. For all but the most exotic of uses bismuth may be considered stable because of its tremendously long half-life.Bismuth metal has been known since ancient times. Before modern analytical methods bismuths metallurgical similarities to lead and tin often led it to be confused for those metals. The etymology of "bismuth" is uncertain. The name may come from mid-sixteenth century New Latin translations of the German words weiße Masse or Wismuth, meaning white mass, which were rendered as bisemutum or bisemutium.
Bismuth subnitrate is a component of glazes that produces an iridescence and is used as a pigment in paint. Bismuth telluride is a semiconductor and an excellent thermoelectric material. Bi2Te3 diodes are used in mobile refrigerators, CPU coolers, and as detectors in infrared spectrophotometers. Bismuth oxide, in its delta form, is a solid electrolyte for oxygen. This form normally breaks down below a high-temperature threshold, but can be electrodeposited well below this temperature in a highly alkaline solution. Bismuth germanate is a scintillator, widely used in X-ray and gamma ray detectors. Bismuth vanadate is an opaque yellow pigment used by some artists oil, acrylic, and watercolor paint companies, primarily as a replacement for the more toxic cadmium sulfide yellows in the greenish-yellow (lemon) to orange-toned yellow range. It performs practically identically to the cadmium pigments, such as in terms of resistance to degradation from UV exposure, opacity, tinting strength, and lack of reactivity when mixed with other pigments. The most commonly-used variety by artists paint makers is lemon in color. In addition to being a replacement for several cadmium yellows, it also serves as a non-toxic visual replacement for the older chromate pigments made with zinc, lead, and strontium. If a green pigment and barium sulfate (for increased transparency) are added it can also serve as a replacement for barium chromate, which possesses a more greenish cast than the others.