Evaluation of cleaning procedures for the conservation of tarnished lead

Abstract

Lead is a soft metal and easy to be damaged during conservation treatments. In this study four different procedures for were assessed: mechanical abrasion with calcium carbonate, immersion in EDTA, potentiostatic reduction in Na2SO4, and potentiostatic reduction and passivation in the same electrolyte. The surface of coupons after six cycles of tarnishing and cleaning was characterized by gravimetry, colorimetry, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). It was observed that all the procedures induced changes on the lead coupons. Mechanical abrasion left a shiny surface but it removed a high quantity of mass; the color of the coupons cleaned with EDTA was similar to original but the surface was completely etched; and the lead reduced potentiostatically presented similar chemical composition to original but the surface was completely covered by re-deposited lead crystals