X-Ray Diffraction Satisfaction

This past Tuesday, I was part of a small group of students who had the opportunity to visit the laboratory of Sonia Mugnaini, a high-energy geologist at UNISI who specializes in work with archaeometric and cultural heritage materials. For about three hours, we had the opportunity to work closely with her on the analysis of several samples. First, our group learned about the Bragg-Brentano diffractometer housed by the university. We prepared a sample of brick from a historical building in Siena using a mortar and pestle. Then, while the x-ray diffractometer was in action, Dr. Mugnaini guided us through the search-match procedures used to identify mineral spectra. Using Bragg’s equation (2dsinѲ=λ) and a printed peak list, my group identified our unknown sample as Pb3O4, a common orange pigment known as Minium. Since I tend to be a hands-on learner, working with Dr. Mugnaini’s XRD instrument greatly increased my understanding of the technique.

Next, we moved to a room that housed the lab’s two polarized-light microscopes. Though all of us had used microscopes in the past, it was an entirely new experience to work with such nice equipment. Polarized-light microscopes allow scientists to observe both transmitted and reflected light, thereby allowing for microstructural identification. After looking a few generic samples of mineral and getting a feel for the instrument, Dr. Mugnaini introduced us to her most current cross-sectional analysis: pigment layers from 13th century frescoes that were recently discovered under Siena’s Cathedral. We looked at samples of flesh, sky, and gold leaf from the frescoes. As we talked, it became increasingly apparent that Mugnaini was completely enthralled with her work; her enthusiasm was contagious! She pulled out samples from Ghiberti's Gates of Paradise and Donatello's David for us to observe and, if we would have had more time, she would have spoken to us all afternoon. It was my favorite academic experience of the trip thus far and made me excited about the prospect of working with people like her in the future.