Solder contains components that vaporize at high temperatures. Different manufacturers use different alloy recipes. One company’s Medium Silver Solder might melt at a different temperature from others.
Since the lower temperature metals basically evaporated, the solder in a joint can “disappear”. Pitting and other surface issues also happen due to this.
Solutions:
Get in, get out.- Use a torch with sufficient heat. Preheat if possible. Silver sucks up heat like nobody’s business and conducts it elsewhere.
Protect seams.- If possible protect seams with yellow ochre or old style whiteout. (Newer types are sometimes difficult to remove.) This isn’t just for preventing parts from soldering together, but helps with vaporizing.
Stay hard.- Use Hard solder for as much as possible. There is less Zinc (or whatever) in Hard solder. That means less evaporation. Since parts of the alloy go up the vent, the melting point of the solder rises. This makes it possible to solder again with the same and NOT melt a joint.
Some of this is more challenging given the intricacies of chains, but you might experiment with solder from different sources.
Ruthanne Robertson