The chloride bearing corrosion products akaganeite ([beta]FeOOH) can form during post-excavation corrosion of chloride infested archaeological iron and is able to corrode iron in contact with it. Its action on iron is examined using [beta]FeOOH synthesized from ferrous chloride and iron powder. Using weight measurements the hygroscopicity of [beta]FeOOH is established. The influence of relative humidity on the corrosion of iron powder mixed with [beta]FeOOH is examined by dynamic mass change within a climatic chamber. At 20[degrees]C and 12% relative humidity, iron in contact with [beta]FeOOH did not corrode. At 15% relative humidity slight iron corrosion was detected after 160 hours, but at 35% relative humidity corrosion occurred after a few hours. Surface adsorbed chloride was removed from [beta]FeOOH by aqueous washing and this reduced its hygroscopity. The reported metastability of [beta]FeOOH was examined via XRD of a 23 year old sample, which was found to be still entirely composed of [beta]FeOOH. These results provide better understanding of [beta]FeOOH corrosion of iron, corrosion control of chloride infested iron using dry storage and the effect of aqueous washing on archaeological iron.