Effectiveness of Electrolytic Treatment in Achieving Stability of Archaeological Metals: A Laboratory and Applied Study

Abstract

This study presents an in-depth experimental investigation of the electrolytic method (Electrolytic Reduction / Cathodic Reduction) as one of the most prominent chemical-physical techniques for the treatment and conservation of archaeological metals (primarily iron, followed by copper and its alloys, and lead) recovered from aggressive environmental contexts such as saline soils or seawater. The research aims to analyse the mechanisms of cathodic reduction of corrosion layers and the removal of harmful ions (especially chloride ions Cl⁻) through electrolytic migration. The process seeks to convert unstable compounds into stable, inert ones, such as magnetite (Fe₃O₄), without causing any damage to the original metallic core.
The study adopted an experimental methodology applied to an archaeological sample consisting of an “iron lamp handle.” The procedure was subjected to precise monitoring of physical and chemical variables, including: electrical potential (E vs. Ag/AgCl reference electrode), pH (between 12.5 and 14), current density (0.005–0.1 A/cm²), and chloride concentration using Ion Chromatography.
Pourbaix Diagrams were employed for the accurate determination of the regions of immunity and passivity within the alkaline environment. The experimental results demonstrated high efficiency, with a reduction in chloride ion concentration ranging from 95% to 99% over a period of 40 to 90 days (depending on the size and thickness of the artefact). This allowed the recovery of fine decorative details and prevented the exacerbation of “bronze disease” or accelerated iron corrosion (β-FeOOH). The electrolytic method proved markedly superior to pure alkaline immersion and traditional mechanical techniques, achieving an additional efficiency of up to 40%, making it the optimal choice and the “gold standard” in archaeological conservation projects in Algeria and the Maghreb region.