Why does freshly cut lead develop a dull gray surface coating?

When lead is freshly cut, it oxidizes rapidly upon exposure to air. This process creates a dull gray surface coating that was historically misidentified as lead suboxide ($P{b}_{2}O$). It is now understood that this layer is actually a mixture of metallic lead and lead monoxide ($PbO$).1

This coating is significant because it serves a protective function, shielding the underlying metal from further corrosion. This inherent chemical resistance is one of the reasons lead is frequently utilized in applications such as roofing, protective coverings for underground or underwater cables, and linings for pipes and conduits used to transport corrosive substances.1