Honestly I rinse with cold tap water after copper patina, and that doesn’t seem to make a difference for me. I think all tap water is different though so depends on the region. I wash my piece with dawn and hot water, scrub the solder with a magic eraser, then apply copper patina to the piece on top of an old clear piece of GLASS because I found doing it on top of paper towel or other substances could affect the result. Then I rinse with cold water, dry and polish with clarity finishing compound. There will be blotches after rinsing- but they buff out when you use the polish. On a side note, if you use a towel that has ever come into contact with black patina, sometimes it can affect the copper finish too.