When the old oil painting are kept in the atmostphere for a long period, the traces of `H_(2)S` gas present in the atmosphere converts lead oxide (PbO) into lead sulphide (PbS) which is black is colour. Therefore, these paintings get transhed. The original whiteness can be restored by keeping then in hydrogen peroxide solution for sometime as a result of which lead sulphide is oxidised to lead sulphate.
`underset("Black")(PbS)+4H_(2)O_(2) to underset("white")(PbSO_(4))+4H_(2)O`
