Soldering each type of solder and alloy has different melting temperatures. The term "silver solder" denotes the type of solder that is used. Some soft solders are "silver-bearing" alloys used to solder silver-plated items. Lead-based solders should not be used on precious metals because the lead dissolves the metal and disfigures it. The distinction between soldering and brazing is based on the melting temperature of the filler alloy. A temperature of 450 °C is usually used as a practical demarcation between soldering and brazing. Soft soldering can be done with a heated iron whereas the other methods typically require a higher
Glass-to-metal seal for nickel and iron and their alloys. This is achieved by heating the metal in vacuum or sometimes in hydrogen atmosphere or in some cases even in air at temperatures above those used during the sealing process. Oxidizing of the metal surface also reduces gas evolution. Most of the evolved gas is produced due to the presence of carbon impurities in the metals; these can be removed by heating in hydrogen. The glass-oxide bond is stronger than glass-metal. The oxide forms a layer on the metal surface, with the proportion of oxygen changing from zero in the metal to the