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Hardened flux that won't pickle off

Hello Orchid family. I am having a problem with a residue after
pickling on sweat soldered pieces. On the edges of the piece
soldered on are left areas that seem like hardened flux that won’t
pickle off. I have used Pripps flux as well as cupronil and I use
Sparex for pickling. I can only get it off with a silicone disc
abrasive. Am I using too much flux? I can’t figure out what is
happening. Any help is greatly appreciated.

Anne Hanson

I would guess that you are not pickling it long enough. The melted
flux hardens into a “borax glass” that is hard to remove
mechanically. Your pickle may not be strong enough or warm enough.
Notice that I said “warm.” You do not want the pickle to boil. It is
not a healthy thing to breath.

Marilyn Smith

Qiuckly quenching the hot work in water will cause the glassy flux
to crack and fall off.


Hi Anne. I often have the same experience especially when using
Pripps and found that “pickling” with a warmed alum solution is the
answer. It seems to dissolve that flux “glass” better than sparex or
pool acid.

Pam Chott

I’ve had that problem, and I’ve found the only way to get it off is
to leave the piece in plain water for several hours or overnight. It
will eventually dissolve.

Janet Kofoed

Actually, it’s said to be better to remove the flux before putting
it in the pickle—keeps the pickle cleaner longer. It comes off
just by boiling it in plain water…! It’s a whole extra step, but
it works…

Janet in Jerusalem