Fwd: APPEAR Project – Portable X-Ray Fluorescence on the Fayum Mummy Portraits

http://www.penn.museum/sites/artifactlab/2016/02/02/appear-project-portable-x-ray-fluorescence-on-the-fayum-mummy-portraits/
mollygleeson wrote:

Hi! This is Eve Mayberger with another update on the Ancient Panel Painting: Examination, Research, and Research (APPEAR) project (see earlier posts here and here). I recently investigated the pigments used on the three Fayum mummy portraits with the portable x-ray fluorescence (pXRF). While the pXRF results for all three portraits are interesting, I am going to briefly discuss the findings for the Portrait of a Woman (E16214).

APPEAR Project, Portrait of a Woman (E16214); Annotation of pXRF test locations

One of the major advantages of pXRF is that it is a non-destructive technique that uses x-rays to identify specific elements. The technique can help to characterize pigments and metal alloy components. It is important to remember that pXRF is a surface technique and will only detect elements present on the surface. I decided to analyze the seven different colors used on the mummy portrait to determine if there are any elemental differences.

Collecting data with the Brucker pXRF

All the test locations recorded prominent peaks for calcium (Ca), iron (Fe), and lead (Pb). Although there is some variation in peak heights across the test spots, it is important to remember that pXRF is a qualitative not a quantitative technique. See below for a representative spectrum for six out of the seven analyzed locations.

APPEAR Project, Portrait of a Woman (E16214); Spectrum for sample #2 – forehead; Peaks detected for Ca, Fe, and Pb

The green used to paint the gemstones on the woman's necklace has an additional peak for copper (Cu). This is not surprising as many greens have a copper component. In ancient Egypt, the greens were generally made with malachite or green earths, or from a mixture of blue and yellow pigments. While malachite is a copper-based compound, more analysis is needed to confidently identify the green pigment used for the gemstones.

APPEAR Project, Portrait of a Woman (E16214); Spectrum for sample #5 – gemstone on necklace; Peaks detected for Ca, Fe, Pb, and Cu

It should be noted that not all pigments can be identified with pXRF alone. Some organic pigments, such as madder, cannot be detected with pXRF. In addition to using analytical instrumentation, it is also important to know what colorants are expected on specific artifacts to help limit the number of possible pigments.

Be sure to visit the blog in the upcoming weeks to read more about the APPEAR project!

Eve Mayberger, Curriculum Intern