I looked at a tub of the Oatey Lead Free Flux, and lo and behold it says it contains Zinc Chloride and Ammonium Chloride. I believe it would tend to be hygroscopic in places where you could not remove all of the residue. Just for the hell of it, I put a dab on the end of a set of junk Baker barrels and heated it to tinning temp. to see what happens when it is left there in our current humid conditions.
Yes, the Baker barrels are really and truly junk. There is an area of very deep pitting across the top of both barrels and the rib. They are otherwise about as nice as you could hope for. It's been a mystery what could have done such bad localized damage and left the rest so nice. A shame.
