Ancient lead paintings are washed with dilute solution of hydrogen peroxide for removal of blackness of these paintaings. On exposure to lead paintings in atmosphere for a long time, lead oxide of paintings reacts with hydrogen sulphide to form lead sulphide. This causes the blackness of the paintings. Hydrogen peroxide changes black lead sulphide to white lead sulphate.
PbS + 4H2O2 ➝ PbSO4 + 4H2O