Joining metals by using a soldering iron to heat the solder until it melts and then, with a flux, running the solder between them. Solder generally comes in strip or wire form. Soft solder is a mixture of tin and lead. Soldering with soft solder is a low-temperature process, which is suitable for joints that will not take a lot of weight or heat. Alloys for hard soldering are made from copper, silver and zinc. The process gives a stronger join, but requires more heat than soft soldering.