A soldering iron is a hand tool used in soldering. It supplies heat to melt solder so that it can flow into the joint between two workpieces. A soldering iron is composed of a heated metal tip (the bit) and an insulated handle. Heating is often achieved electrically, by passing an electric current (supplied through an electrical cord or battery cables) through a resistive heating element. Cordless irons can be heated by combustion of gas stored in a small tank, often using a catalytic heater rather than a flame. Simple irons, less commonly used today than in the past, were simply a large copper bit on a handle, heated in a flame. Solder melts at approximately . Soldering irons are designed to reach a temperature range of . Soldering irons are most often used for installation, repairs, and limited production work in electronics assembly. High-volume production lines use other soldering methods. Large irons may be used for soldering joints in sheet metal objects. Less common uses include pyrography (burning designs into wood) and plastic welding (as an alternative to ultrasonic welding). History Before the development of electric soldering irons, the typical soldering iron consisted of a copper block, with an appropriately shaped point, supported on an iron rod and held in a wood handle. Immediately before use, the iron was heated over a fire or in a charcoal brazier, and it had to be reheated whenever it became too cool for use. Soldering irons were primarily used by tinsmiths and coppersmiths to work with thin sheet metal. A large copper block was required in order to have sufficient thermal capacity to provide useful heat after removal from the fire, and copper is expensive. This led to the development of soldering irons that had a small copper tip attached to an inexpensive cast-iron block. Some irons even had removable and replaceable copper tips. The first electric soldering iron had a very lightweight platinum tip heated by electric current flowing through the tip itself. By 1889, electric soldering irons were being developed with a resistance wire wrapped around the back end of the copper head and enclosed in a protective shell. Alternatively, the heating element could be enclosed in a relatively light-weight hollow copper head. In 1894, the American Electrical Heater Company began manufacturing electrical soldering irons on a large scale in Detroit. They started producing them shortly after American Beauty released