We had the lead tray in our chimney replaced about 18 months ago. The chimney was taken down to tray level and then rebuilt incorporating a new tray. There is a big apron that sticks out and has been banged down around the chimney.
I have noticed that this lead over hang appears to have yellowy green deposits on it. They appear to be running down the lead a bit like water deposits. We had the flashing replaced about 4 years ago and that looks perfectly fine although the yellowy green deposits from the tray seem to be running down onto the lead flashing and it looks very unsightly.
What is it and how can I stop it from getting any worse?