Underwater excavations on a 16th-century shipwreck off villefranche (france) retrieved many different materials, generally well-preserved in the sand. There were large pieces of artillery covered with a thick hard corrosion layer. The presence of chlorides led to rapid destruction once the objects were out of the sea environment. The project began, after a literature survey, by trying out classical methods for removing corrosion products and ended by suggesting a simple, efficient electrochemical method. Electrochemical dechlorination of underwater finds had not before (1983) been carried out in france. The drop in chloride concentration was followed by micro-analysis. It is recommended that pieces be kept in sea-water until cleaned, then immediately desalinated before cleaning and adding a protective layer. Charts, graphs, diagrams, tables and colour illustrations.