Tungsten is a metal with a wide range of uses, the largest of which is as tungsten carbide (W2C, WC) in cemented carbides. Cemented carbides (also called hardmetals) are wear-resistant materials used by the metalworking, mining, petroleum and construction industries. Tungsten is widely used in light bulb and vacuum tube filaments, as well as electrodes, because it can be drawn into very thin metal wires that have a high melting point. Other uses: A high melting point also makes tungsten suitable for space-oriented and high temperature uses which include electrical, heating, and welding applications, notably in the GTAW process (also called TIG welding). Hardness and density properties make this metal ideal for making heavy metal alloys that are used in armaments, heat sinks, and high-density applications, such as weights, counterweights, ballast keels for yachts and tail ballast for commercial aircraft. The high density makes it an ideal ingredient for darts, normally 80% and sometimes up to 97 %. This allows darts containing tungsten to have a smaller diameter than those of other metals at the same weight, permitting tighter groupings. High speed steel contains tungsten and some tungsten steels contain as much as 18 % tungsten. Superalloys containing tungsten are used in turbine blades and wear-resistant parts and coatings. Examples are Hastelloy and Stellite. Tungsten powder is used as a filler material in thermoplastic composites which are used as a nontoxic substitute for lead, in bullets, shot, and radiation shields. Tungsten chemical compounds are used in catalysts, inorganic pigments, and tungsten disulfide high-temperature lubricants which are stable to 500 °C (930 °F). Since this element's thermal expansion is similar to borosilicate glass, it is used for making glass-to-metal seals. It is used in kinetic energy penetrators, usually alloyed with nickel and iron or cobalt to form tungsten heavy alloys, as an alternative to depleted uranium. Tungsten is used as an interconnect material in integrated circuits. Contact holes are etched in silicon dioxide dielectric material, filled with tungsten and polished to form connections to transistors. Typical contact holes can be as small as 65 nm. Tungsten carbide is one of the hardest substances in existence and is used in, among other things, machine tools such as milling cutters. Tungsten carbide is the most common material used to make milling and turning tools, and used together with cobalt and carbon is often the best choice for such applications. Used extensively for shielding in the Radiopharmaceutical industry. It is often employed when transporting individual FDG doses (called 'pigs') - the high energy of Fluorine-18 makes lead much less effective. Tungsten is used in the emitters of focused ion beam and electron microscopes. Tungsten is also beginning to see uses in jewelry. Its hardness makes it ideal for rings that will never scratch, and will in turn not need polishing (this is especially good for brushed designs). Miscellaneous: Oxides are used in ceramic glazes and calcium/magnesium tungstates are used widely in fluorescent lighting. Crystal tungstates are used as scintillation detectors in nuclear physics and nuclear medicine. The metal is also used in X-ray targets and heating elements for electrical furnaces. Salts that contain tungsten are used in the chemical and tanning industries. Tungsten 'bronzes' (so-called due to the colour of the tungsten oxides) along with other compounds are used in paints. Tungsten Carbide has recently been used in the fashioning of jewelry due to its hypoallergenic nature and the fact that due to its extreme hardness it is not apt to lose its luster like other polished metals. Some types of strings for musical instruments are wound with tungsten wire.