The restoration and preservation of metallic archaeological objects made of ferrous materials require the elimination of the chlorinated components contained in the corrosion products. Otherwise, after excavation of the artefact, corrosion will continue, sometimes at an accelerated rate. Different treatments may be applied for that purpose: electrolytic or alkaline sulphite baths, cold hydrogen plasma. This paper describes the hydrogen plasma treatment reactor in use at the Archaeological Museum of "Val d'Oise" , in France. Results of plasma treatments on artefacts are presented, together with optical measurements made at the reactor during the treatments.