Oxidation is a natural process which affects many materials including lead, when exposed to varying environmental conditions. Those conditions, rain, snow or any other weather cycle will determine the degree of severity of oxidation and the time scale over which it will occur.
Oxidation is far more likely to occur during winter conditions, with the weather attacking the shiny surface that the lead strip has when first applied to glass. The natural colour of lead is a matt grey, so it is both normal and inevitable that discolouration will occur. This process although common knowledge to anyone within the industry is not always familiar to the householder.
Questions always arise about oxidation, the most common being “How long will it take my lead to oxidise and look like my neighbours?”. The answer cannot be given truthfully by anyone. Only the weather conditions can determine this.
During the oxidation process it is not uncommon for different colours of bronze, blue or even gold to become visible. Once this has happened, it is a sign that the lead strip is forming its own protective barrier.
Normal cleaning of the windows with warm water and washing-up liquid will ensure that the lead is kept clean and natural oxidation can take place.
The time of year will have an effect on how the lead will react, but by no means should there be any concern about the appearance, as this natural process will always take place.