Quoted:
Trust me on this guys - the ONLY thing that can be used to clean copper before soldering is sandpaper, the red or tan abrasive kind that has ONLY MINERAL abrasive glued to it. You CANNOT use a stainless brush, black iron brush, steel wool, or stainless curly scouring pads to clean a copper joint. Metal from the brush, steel wool, or curly pad will transfer to the copper and form a MICROSCOPIC METAL FILM on the copper that SOLDER WILL NOT STICK TO. When you use METAL to clean a copper joint you leave behind a MICROSCOPIC METAL FILM ON THE COPPER, no matter how clean and shiny the copper looks.
Metal abrasives on copper is a 100% guaranteed soldering failure.
I've used steel wool, emery cloth, silicon carbide abrasive paper, aluminum oxide abrasive paper and wire brushes to clean joints without any problems.
I don't see why they should pose problems, since many other metals besides copper can be soldered with the correct flux, etc. I wonder if it's actually some of the glue used to bond the abrasives to the papers that causes more problems than the actual choice of abrasive material.
Not disputing your experience, just wondering out loud..
I do suspect that the detergents in steel wool scouring pads would certainly cause problems, though...