I have a new glazed porcelain floor in my kitchen that was driving me crazy because any drop of water would leave a mark or smudge if it wasn't wiped up right away. I couldn't understand why cleaning didn't get rid of these stains. it turns out there was a residue on the surface from one of the Spray on/wipe off tile and stone cleaners. I used FilaPS87 from Fila surface care solutions which I had ordered before I had tile installed and forgot about it. It worked perfectly and now the tiles are stripped of the the residue and clean. Now I can use just hot water to clean and use the Fila intensive cleaner only when necessary. I think many porcelain problems might come from residue forming from various products on the surface-my two cents!