The corrosion of the lead surface is responsible for it losing its lustre.
The metals lose their shine on brightness on keeping in the air for a long time due to the formation of a thin layer of oxide, carbonate or sulphide on their surface by the slow action of various gases present in the air.
- Sodium loses its lustre on exposure to air due to formation of Na2O, NaOH and Na2CO3Sodium on exposure to air catches the O2,H2O(vapour) and CO2 and forms Na2O, NaOH