During the soldering process, the metals are heated with the torch. As the temperature increases, microscopic spaces open up in the crystalline structure of the metal. When the melting temperature of the solder is reached, it flows into the seam (ideally) and actually penetrates both pieces of metal. When the heat is removed, the structure of the metal returns to normal, with the solder fully integrated into the metal. This provides a strong bond between the two pieces of metal. "Soft" solder, as mentioned earlier, does not have this effect. The low temperature involved does not cause the structure of the metal to open up, so the solder just sits on the surface, and does not provide a true bonding.
Author: Dave Sebaste
ArtMetal Editor: enrique
Last Updated: Tue, Sep 17, 1996