Koraks is correct, fungus has eaten into the coating and no amount of cleaning will bring it back. It could be polished to a nice clean state, but that would remove what coating is left. Of course you could always have it polished and pay to have it recoated. This is one of Schneider cheaper enlarging lenses and the polishing and reciting thing is just not worth the cost. If it were me I'd forget this lens and buy the next level up in Schneiders line of enlarging lens, which is the Componon or better yet a Componon-S. Of course you could just continue to use it and probably wouldn't see a difference in results.