Soldering joins two pieces of metal, such as electrical wires, by melting them together with another metal to form a strong bond. Many people use this technique in their field, from electrical engineering and plumbing to jewelry and crafts. In a delicate procedure, a special material, called solder, flows over two pre-heated pieces and attaches them through a process similar to welding or brazing.
The process of soldering is tricky and intimidating in practice, but easy to understand in theory. Basic supplies include a soldering iron, which is a prong of metal that heats to a specific temperature through electricity, like a regular iron. The solder, or wire, is often an alloy of aluminum and lead, and needs a lower melting point than the metal that is being joined. Finally, a person performing this technique needs a cleaning resin called flux that ensures the joining pieces are incredibly clean. Flux removes all the oxides on the surface of the metal that would interfere with the molecular bonding, allowing the solder to flow into the joint smoothly.
The first step in soldering is cleaning the surfaces, initially with sandpaper or steel wool, and then by melting flux onto the parts. Sometimes, flux is part of the alloy of the wire, in an easy to use mixture. Then, the pieces are both heated above the melting point of the solder (but below their own melting point) with the iron. When touched to the joint, this precise heating causes the wire to "flow" to the place of highest temperature and makes a chemical bond. The material shouldn't drip or blob, but spread smoothly, coating the entire joint. When it cools, it produces a sturdy, even connection.
Various metals can be soldered together, such as gold and sterling silver in jewelry, brass in watches and clocks, copper in water pipes, or iron in leaded glass stained windows. All these metals have different melting points, and therefore use different solder. Some "soft" wire, with a low melting point, is perfect for wiring a circuit board. Other "hard" solder, such as for making a bracelet, needs a torch rather than a soldering iron to get a hot enough temperature. Electrical engineers and hobbyists alike can benefit from learning the art and science of this process.