How do you guys hand lead chimney flashings? Sometimes they oxidize horribly from the roof chems. I know from experience that it's only temporary but is there a way to prevent this? Would bleach wash help at all? Sometimes the chimneys are just plain inaccessible, so using a shield to cover them is not always possible.

The picture I attached is a perfect example, showing where I sprayed the chemicals that the flashings turned brown almost immediately. I would love to remedy this problem. Sometimes I can block them with a piece of plywood and keeping them wet does not alleviate the problem much.

Thanks