Note that the "Heat" of ordinary hot salts bluing does not melt the solder. It is the chemical reaction of the Lye with the lead/tin solder which eats it away. It will also devour aluminum.
This begs this next question:
Why do you see Lye sometimes used as either a degreaser or neutralizer when refinishing double gun barrels? I've never considered using it, but it's sometimes mentioned. Is it merely a matter of strength? How is Lye used during the Hot process? I'm fairly unfamiliar with the Hot process, since I can't ever see a reason to use it.
This is one of those "nice to know" questions...
Regards
