The use of radiography and GIS to assess the deterioration of archaeological iron objects from a water logged environment

Pollution, acid rain, and modern agricultural practise are often blamed when archaeological metal objects are heavily deteriorated. However, looking at a deteriorated object, it can be difficult to differentiate whether the deterioration took place recently, or maybe hundreds or even thousands of years ago. A detailed knowledge of the changing environmental conditions of the archaeological site, a large number of objects, and a reliable measure for the state of preservation of the objects are necessary to assess the deterioration history.
In this paper an analytical method based on X-ray radiography is used to give an objective measure for the state of preservation of iron objects. It is demonstrated that the method is robust, independent of the operator, and has good precision. With this tool and applying the use of GIS, 151 lances from a water logged environment (Nydam, Denmark) were studied, to see if it was possible to correlate the state of preservation with the exact find location, the year of excavation or the method of deposition. Apparently, in this case the method of deposition was most important, so that the deterioration pattern observed today is decided during the first few years after deposition, which took place in 200e500 AD. It has not been possible to demonstrate an increased deterioration from the first excavations in 1859 until today.
The work is part of a major project in Nydam, which has also involved studying corrosion products, deterioration of modern materials, environmental parameters, and the effects of archaeological excavations.