This paper presents the results obtained in the ODéFA project funded by the French Ministry of Culture. This project aims to understand the effect of the dechlorination methods daily used in conservation laboratories on archaeological iron. Two treatments are considered: immersion and electrolysis in alkaline solutions. Samples are archaeological iron artefacts from the same marine site. They were analysed with a combination of microbeam characterisation tools (Raman and Fourier transform infrared microspectroscopies, micro X-ray diffraction and energy dispersive spectroscopy) before, during and after treatment. The experiments show the presence of: ?-Fe2(OH)3Cl and ?-Fe2(OH)3Cl. During treatment, chlorides are localised at the metallic interface and around inclusions in the metal. The corrosion layer is mainly a mix of goethite (?-FeOOH) and oxyhydroxides (feroxyhite and/or ferrihydrite) and magnetite (Fe3O4). The same corrosion layouts are identified during the immersion or electrolysis. The electrolysis removes twice as much chlorides as the immersion method.