Conservation of ancient lead artifacts corroded in organic acid environments: electrolytic stabilization/consolidation

Abstract

An electrolytic reduction treatment using cathodic polarization at constant potential was applied to heavily corroded lead objects which had been exposed for a long time to corrosive organic acid vapours. Experimental conditions were determined through chemical and electrochemical tests conducted on artificially carbonated commercial lead coupons and then on lead objects from public collections. The electrolytic procedure tested consists of polarization at −O·9V versus SCE in O·5M sodium sulphate (Na₂SO₄) solution, the counter-electrode being modified according to the size and nature of the object to be treated. The logarithm of the reduction current versus time of treatment [log(

I_red|) = g(t)] curves were plotted to determine the effectiveness of the treatment. Subsequent exposure to hydrogen plasma was found not to improve the treatment.