X-ray Fluorescence and Raman Spectroscopy Help Uncover Archeological Facts

Portable X-ray fluorescence (XRF) and portable Raman spectroscopy techniques have come a long way in recent years, helping researchers analyze more samples in the field than ever before. One such researcher, Mary Kate Donais, who is an associate professor in the Department of Chemistry at Saint Anselm College in Manchester, New Hampshire, recently spoke to Spectroscopy about her innovative research using portable XRF and Raman spectroscopy at an archaeological excavation site in Italy.

Spectroscopy: How do you use portable XRF and portable Raman spectroscopy in the archaeological excavation work you’ve done in Italy?

Donais: We've used both techniques thus far but have much more experience with portable XRF. The portable XRF instrument has been used in the field for in situ measurements and in our lab for analyses of artifacts removed from the site. The data are used mostly for material comparisons to answer questions such as, "Is the mortar on this wall similar to the mortar on this wall?" By answering a question like that, we can help the site archaeologists decide whether two walls were likely constructed at the same time or not. Thus far, the portable Raman instrument has been used together with the portable XRF system to identify pigments on fresco fragments.

Spectroscopy: How do the two methods complement each other?

Donais: With XRF being an atomic technique and Raman a molecular technique, they are very complementary and are a valuable pair of instruments for work with pigments. They usually allow for confident identification of pigments. We hope to extend that to pottery fragments during our next excavation season.

Spectroscopy: How do the results compare with those obtained using flame atomic absorption?

Donais: Portable XRF data have been compared to many traditional laboratory-based measurement techniques such as flame atomic absorption spectroscopy (FAAS), inductively coupled plasma (ICP), inductively coupled plasma–mass spectrometry (ICP-MS), and instrumental neutron activation analysis (INAA). For our work, we couldn't possibly use any of the destructive lab-based techniques due to the cultural value of many of our samples and the inability to move many of our samples to a lab. It is much more valuable for us to conduct in situ analyses at many locations along a structural wall than to remove a smaller number of samples to a lab.

Spectroscopy: Has the use of these methods led to any major discoveries or breakthroughs?

Donais: For our site, we've been able to establish the continuity of a major structural wall without excavating its entire length. We've also been able to confirm ancient repairs to walls. In general, I feel our use of portable XRF for in situ material differential and archaeological phasing is a breakthrough.

Spectroscopy: Would it have been possible to do the same level of research before the advent of portable systems?

Donais: Absolutely not. Only so much could be achieved by removing samples to a lab. We can do so much more by bringing the instrument to the sample.

Spectroscopy: How could the portable instruments be improved with additional features to be more useful in your research?

Donais: Wireless transfer of data from the instrument to a computer would be great. Right now we have to use great care in the field because the instrument is attached by a data cable to our laptop. We don't need the laptop taking a tumble into a trench! The screen size on the on-board instrument computers are too small, so we choose to use a laptop to evaluate and view the data as it's collected. So, one researcher operates the instrument and another operates the laptop. They constantly communicate during data collection to ensure the integrity of both the equipment and the data.

Spectroscopy: Are there any other research areas in which you plan to use portable XRF or Raman with your students?

Donais: As I mentioned earlier, we plan to expand into examinations of pottery using both portable XRF and Raman during our 2013 season. Our research team (Saint Anselm College in association with the Institute for Mediterranean Archaeology in [add city and country]) also has expanded into a second site, a subterranean structure carved in a pyramidal form under the city of Orvieto, Italy, Cave 254. We plan to expand our portable instrumentation work to include both sites.

Spectroscopy: How do you see portable XRF and Raman being used in future spectroscopy research applications?

Donais: As more people become aware of the portability of the techniques, their use will certainly expand into all sorts of research areas. In addition, these instruments can be relatively affordable while also being nondestructive and easy to use. I think this makes them a great fit for undergraduate teaching and research. As far as new applications, I can't fathom a guess. A lot has been done, but who knows what new materials or samples are out there!