Copper oxidizes quickly, you need to clean it shiny just before you do the transfer. I use an old T-shirt to hold and handle the board, to avoid finger prints. Mostly I use steel wool, then wipe it down with a little acetone (same stuff I use to remove the toner after the etch). Seldom got a bad board, until... I bought a refilled (recycled) toner cartridge, now I get millions of tiny pinholes. Not pretty, like before, but they still work. Definitely not worth saving $23. Guess it's okay for printing memos, not so good for low volume home use, crap for PCBs.