H₂O₂ restores the colour of old lead painting , blackened by the action of H₂S gas, by:

Lead is present as Pb²⁺ and when H₂S comes in contact with Pb²⁺, it forms PbS (black). This PbS is responsible for the blackening of the painting. To remove this blackness, paintings wash with H₂O₂, where H₂O₂ converts PbS (black) into PbSO₄ (white). This helps in restoring the color of the old paintings.

$\underset{\mathrm{Black}}{\mathrm{PbS}}+4{\mathrm{H}}_2{\mathrm{O}}_2⟶\underset{\mathrm{White}}{{\mathrm{PbSO}}_4}+4{\mathrm{H}}_2\mathrm{O}$