I use renaissance wax too. I first lightly brush over the piece with my finger to remove the loose bits of patina and salts. Then I gently apply the RW with my finger and give it a quick, gentle buff with a soft cloth.
I used RW on this copper disc. I darkened the disc with liver of sulfur first. The patina probably did turn a little green after applying the wax, but still good color on the finished piece.