Identification of Corrosion Mechanism and Preventive Conservation Approach in Archaeological Iron Objects from “Pahlooj” Site, Savadkouh, Mazandaran

Characterization of chemical and microscopic features of corrosion layers covering archaeological iron objects is an important subject to understand conservation conditions of the archaeological metals and to help conservators for decision-making for long term preservation of archaeological objects. There are many archaeological iron objects in museum collections that are discovered from different archaeological excavations. Iran is one of the important regions in ancient metallurgy and many metallic objects and collections have been found from archaeological sites from different periods of this region. In this paper, an analytical study was established and undertaken on the corrosion layers and products on some archaeological iron objects to identify corrosion morphology and mechanism occurred during the long term burial time. The iron objects are discovered from archaeological excavation from “Pahlooj” a Sasanian cemetery in Savadkouh region, Mazandaran, northern Iran. The iron objects are now maintained in Kolbadi museum of Sari, the capital of Mazandaran province. The corrosion morphology and mechanism were observed and examined in these iron objects by optical microscopy (OM), Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy (SEM-EDS), X-ray radiography as well as X-ray Diffraction (XRD) analytical methods. The results showed that a thin corrosion crust has been formed on the surface of the metal. The corrosion crust observed in the samples presents a multiple layer structure that may be formed due to changes occurred during burial time as well as post-excavation conditions. The main corrosion products are consisting of different iron oxides and hydroxides. In fact, the corrosion morphology and mechanism of the iron objects of Pahlooj archaeological sites is due to long-term burial in a moderately corrosive soil environment. The aim of identifying deterioration process is to propose preventive conservation matter and provide proper situation prior and during excavation. Providing proper situations for storing samples after excavation need to obtain a situation with low amount of oxygen and humidity. One of the methods in this matter is to use moisture absorbers.