X-ray fluorescence (XRF) has emerged as a common technique for non-invasive analysis of the elemental composition of cultural artifacts. In a new study, published in the journal Spectrochimica Acta Part B: Atomic Spectroscopy a group of researchers from the Università degli Studi di Milano-Bicocca in Milan, Italy used this technique to analyze Puebla ceramic decorations (1). The team analyzed Puebla Policromo, which is a style of glazed ceramic that originated in Puebla, Mexico.
XRF is a common technique in the elemental analysis of art and other artifacts. Portable devices make it easy for scientists to quickly and non-invasively analyze works of art in museums or archaeological sites. The analysis is completed by irradiating a sample with high energy X-rays (2). The technique is commonly used in industries including oil and gas, automotive, aerospace, mining, and construction (2).
For successful XRF analysis samples must be flat and homogenous for the best results, which can be a challenge with many artifacts, such as ceramics, which often have many layers and pigments. The research team used angle resolved XRF (AR-XRF), which is an analytical technique where a sample is irradiated via different angles.
“Historical, and archeological artifacts are, most of the time, inhomogeneous samples, not only because they can be made of different materials (like ceramics or pigments), but also because they can exhibit layers that are considered ‘intermediate’ thickness for the investigated x-ray energies,” the scientists wrote in the study. “These layers may originate from the manufacturing of the sample, such as glazes covering a ceramic object, or the gilding of a metal; but also, be the result of changes in surface composition caused by aging and other alteration processes (1).”
The decorations on the sample were classified into three groups: black spots, blue decoration, and black stripes, on top of a homogenous thick white glaze. The scientists were able to determine the composition of the white glaze, which was made of mostly lead (Pb) and tin (Sn). They also found the blue decorations had a similar composition with the addition of cobalt and iron. The black decorations showed intense signals of iron and low signals of lead, they wrote.
However, using the AR-XRF to analyze Puebla ceramic decorations proved challenging, the scientists noted. The information they were able to glean from the technique largely depended on the parameters and thickness of the layers.
“In the case of the blue glaze, AR-XRF cannot discriminate the presence of two different layers,” they wrote. “Indeed, in this case, the colored glaze is very thick, and the composition is similar to that of the white glaze underneath, besides, a diffusion of the blue glaze inside the white glaze can also be observed in the fractures. For this reason, the blue-colored regions are described as a unique layer of infinite thickness (1).”
While AR-XRF can be employed to analyze the structure of a layered sample, it won’t be able to give complete information on the composition and thickness of different layers, they wrote. Other techniques, including Rutherford backscattering spectroscopy (RBS) coupled with particle induced X-ray emission (PIXE) may be better suited for the analysis of layered samples.