[Nuvistor]

Some emery paper leaves an oily residue, first rule with soldering is everything as to be clean, i do like other scrape the wire clean.

I cannot find the report now but a housing estate was troubled with failed copper water pipe joints, the copper pipe and joints were top quality, the investigators found the problem of a plumber using a type of emery paper that left an oily residue that ruined the internal soldered joint in the couplings.