The thermal treatment of corroded iron objects for the purpose of removing chloride with subsequent conservation can be performed in hydrogen gas, air, or inert gas atmosphere. Because there is a danger of explosion in the case of the hydrogen method, it is suggested to heat the objects to about 700°C in a nitrogen atmosphere. The examination for completeness of treatment is carried out through color reaction by means of salicylic acid methylester. The objects are finally preserved with wax or an acrylic resin in vacuo.