melting temperature of tin-lead solder can damage many crystals, a fusible alloy with a low melting point, well under , such as Wood's metal was used. One surface was left exposed to allow contact with the cat-whisker wire. Cat whisker: Phosphor bronze wire of about 30 AWG / 0.25 mm diameter was commonly used as a cat whisker because it had the right amount of springiness. It was mounted on an adjustable arm with an insulated handle so that the entire exposed surface of the crystal could be probed from many directions to find the most sensitive spot. Cat whiskers in homemade detectors usually had a simple curved shape, but most professional cat whiskers had a coiled section in the middle that served as a spring. The crystal required just the right gentle pressure by the wire; too much pressure caused the device to conduct in both directions. Precision detectors made for radiotelegraphy stations often used a metal needle instead of a "cat's whisker", mounted on a thumbscrew-operated leaf spring to adjust the pressure applied. Gold or silver needles were used with some crystals. Carborundum detector Invented in 1906 by Henry H. C. Dunwoody, this consisted of a piece of silicon carbide (SiC, then known by the trade name carborundum), either clamped between two flat metal contacts, or mounted in fusible alloy in a metal cup with a contact consisting of a hardened steel point pressed firmly against it with a spring. Carborundum, an artificial product of electric furnaces produced in 1893, required a heavier pressure than the cat whisker contact. The carborundum detector was popular because its sturdy contact did not require readjustment each time it was used, like the delicate cat whisker devices. Some carborundum detectors were adjusted at the factory and then sealed and did not require adjustment by the user. It was not sensitive to vibration and so was used in shipboard wireless stations where the ship was rocked by waves, and military stations where vibration from gunfire could be expected. Another advantage was that it was tolerant of high currents, and could not be "burned out" by atmospheric electricity from the antenna. Therefore, it was the most common type used in commercial radiotelegraphy stations. Silicon carbide is a semiconductor with a wide band gap of 3 eV, so to make the detector more sensitive a forward bias voltage of several volts was usually applied across