Just been discussed in another thread but I can't find it just now!
[Could even have been you]
This is due to the flux used to clean the joint during soldering.
'Wiping whilst hot' is apparently a shooting offence.
If the acid flux is cleaned off it should not come back (hopefully).
I would assume that warm water and a mild detergent would shift it.
Don't know if you have to neutralise it to prevent it coming back from
If so, presumably some weak alkali solution (although I suppose that could
cause other problems) :-(
Spray with something like WD40 to clear any remaining water based solvents?
Or just polish every day with Brasso :-)
Hopefully someone has a tried and tested cure.
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