27/09/2005

Collaboration between the Archaeometry Laboratory of the University of the Aegean and the Electronics Department of the Technological Educational Institute (TEI) of Lamia has resulted in a new method for more accurate dating of archaeological artifacts, using Secondary Ion Mass Spectrometry (SIMS) on obsidian hydration.

The subject of the scientific field of archaeometry is the application of exact or natural sciences (physics, mathematics, geology, astronomy, biology, geophysics) in the study of archaeological problems. Specific methods and techniques are applied on archaeological material and allow us to date the material, analyse its components, determine its origin, perform a comparative study of various finds, locate buried artifacts without excavation and interpret and reconstruct their environment.

One of the methods used for dating archaeological artifacts is the obsidian hydration method, using this acidic rock derived exclusively from volcanic areas of a relatively young geological age.

This method is based on the diffusion of environmental water (humidity) into the obsidian mass. A layer of hydration is formed within the rock, its width varying according to the time of water penetration, environmental temperature and humidity, and its particular physicochemical structure. The longer diffusion lasts, the older the rock is.

This method?s major disadvantage is the fact that diffusion depends on the hydration rate, i.e. the rate of water penetration, in μm/year, a factor that changes according to the environmental temperature and humidity. These conditions cannot be determined for archaeological time periods, and therefore the results are not reliable.

The new technique was developed at the University of the Aegean (Department of Mediterranean Studies, Laboratory for Archaeometry, Professor I. Lyrintzis), while the relevant software was developed at the TEI of Lamia (Department of Electronics, Assoc. Professor Th. Ganetsos). The solution of the problems explained above is based on a differential equation, which describes the physicochemical phenomenon of water diffusion and is based on the distribution of the amount of water molecules in depth, i.e. on the diffusion profile. A critical factor in this diffusion model is a saturated surface layer, which reaches a specific diffusion depth.

The exact measurement of the distribution of water molecules by diffusion depth is performed using the SIMS nuclear analysis method, since light microscopy methods are not adequate. The SIMS method can analyse differences in concentration within a few nanometres, for a large range of chemical elements and at depths ranging from tens of nanometres to several micrometres.

The analysis method is based on the spectroscopic examination of (secondary) ions emitted from a specimen, when it is focused and bombarded by a ray of primary ions. The type and composition of these secondary ions represents the type and composition of the bombarded specimen surface, and therefore the spectroscopic mass analysis of these ions can allow quantitation of the elements, and specifically of hydrogen (H+), present in the volume under analysis. The depth of water penetration and its concentration, as determined based on the concentration of hydrogen versus the depth from the surface, can differ according to the type of obsidian and environmental temperature.

A characteristic result is the dating of a specimen from the area of Strofilas on the island of Andros. Carbon-14 gave an age of 4,700 to 6,000 years before today, while the SIMS-SS method (obsidian hydration with SIMS spectrometry and emphasis on the SS saturation area) gives a precise age of 5594 ± 50 years.

According to Dr Th. Ganetsos, "This new technique and the relevant software have already attracted the interest of many companies and archaeology museums, during exhibitions relevant to this field; this Greek innovation were presented both at the 21st Pan-Hellenic Conference of Solid State Physics & Material Science (28-31 August, Nicosia, Cyprus), and at the international SIMS Conference - Symposium on Archaeometry (12-16 September 2005, Manchester, U.K.). Furthermore, from 20 September to 20 October 2005, a post-graduate student from a Japanese university was trained at the TEI of Lamia in the use of the method?s software, and will use the method in his doctoral dissertation on obsidian specimens from Japan."

Source: TEI of Lamia, University of the Aegean