Richard I find boracic acid good mix with water to a paste then
brush over any surfaces that could get to hot. Its also a great
flux sulpheric acid 1 to 6 will remove any residue. This is all I
use for flux now its also great for protecting diamonds best
If you mix the boric acid powder with alcohol instead of water,
you can burn off the alcohol and leave the boric acid on the
piece that you are soldering. I would still yse a flux at the
solder
Rick Hamilton
Richard D.
Hamilton,Jr.
Goldsmith