Corrosion of archaeological material is often inhibited in situ by concretion and removal can cause accelerated attack through allowing ingress of oxygen, particularly when Cl is present. Field methods of treatment for passivation are described, to maintain the artefact in good condition before pretreatment to remove the surrounding layers of foreign material. Conservation methods discussed include acid pickling, use of sequestering agents, aqueous washing, and electrolytic reduction. Subsequent stabilisation techniques are dealt with and the H reduction process developed for the Mary Rose artefacts is treated in detail.