Relics such as mummies must be examined very carefully to avoid causing any damage, and many methods have been attempted to get a clear glimpse into their unique past. For mummies in particular, computed tomography (CT) scanning, magnetic resonance imaging, and terahertz imaging have previously been used; however, these methods are unable to identify the crystalline materials present.
X-ray diffraction (XRD) is a method commonly used to characterize materials and identify the crystalline phases present. One of the reasons this method is useful is because it is nondestructive, meaning that measurements can be performed without damaging the sample. In a recent study, researchers S.R. Stock, M.K. Stock, and J.D. Almer successfully applied XRD in conjunction with CT to glean new information about a 1900-year-old mummy without having to unwrap it.
XRD had been used to investigate samples extracted from mummies in the past, but this study is unique in its ability to examine materials within intact mummies. Hailing from Northwestern University, Metropolitan State University of Denver, and Argonne National Laboratory, the team investigated a Roman-era Egyptian portrait mummy called Hawara Portrait Mummy 4 (HPM4), using CT-guided synchrotron XRD mapping to identify regions of interest.
Although CT scans had previously been performed on this mummy, the group’s new CT results provided insight into details that were only observable in low contrast on the earlier x-ray films. Most significantly, the age and sex of the person within the wrappings could now be confirmed. The portrait painted on the mummy depicts a young woman, but at a height of 937 mm, the size of the mummy is more suggestive of a child’s body than an adult’s. By using CT data, the researchers could observe the skeletal and dental development at the time of death, as well as the genitalia, corroborating the perceived age and sex of the subject as a young girl.
They noted that most of the bones that fuse during development were still separate within the skeleton; however, since the level of skeletal development could potentially be altered by malnutrition or other environmental factors, a more accurate determination could be made by examining the teeth. In their study, the authors state that the full set of primary teeth was present and had not been shed, and the permanent teeth had not yet emerged. Within the bony crypts that house the first and second permanent molars, developing crown enamel could be seen. Thus, the researchers could strengthen the assertion that the age at death was 5 ± 0.75 years, aligning with both the height of the skeleton and the aforementioned bone development.
According to the authors, one possible reason for the dissonance between the portrait and the individual is that the artist was imagining the child in the future as a young adult. Alternatively, it is possible that some of the portraits used on mummies to depict the deceased may not be entirely accurate. This makes the group’s CT and XRD analysis very useful, as the methods were used to assess the age and sex of the individual without having to disturb the wrappings. This could aid future studies in classifying different mummies, especially since many mummies do not feature portraits on the exterior.
Utilizing a beamline at the Argonne National Laboratory, the researchers conducted XRD on areas of interest within the mummy. They were able to locate specific inclusions thanks to the CT roadmap that they had developed previously. Due to the large sample size, it would have been impractical to perform diffraction on the entire mummy, especially given the time constraints of the study; thus, the researchers made use of vertical and horizontal translation across the beam, in conjunction with their roadmap, to analyze objects of interest. They had only 16 hours of data collection time, with each diffraction pattern taking 4 seconds to collect. This shows the speed with which XRD experiments can be carried out, making it possible to collect many distinct patterns in a short period of time.
One of the study’s findings involved wires within the mummy, presumably used to stabilize the outer layers of linen during earlier conservation. By performing XRD on these wires, it was possible to identify the wires as a modern dual-phase steel containing austenite and ferrite phases. They were also able to confirm the length of the wires as 33.7 ± 3.7 mm, which is similar to the size of commercial pins typically used on specimens. Moreover, the diameter of the steel specimen pins, as identified from the CT data, aligned with the diameter of the commercial pins.
Another region of interest was an object dubbed “Inclusion F” in the linen above the girl’s abdomen. The object is positioned at the level of the fourth lumbar vertebrae. Based on the positioning and the size of the inclusion, it is consistent with scarabs observed in other mummies via CT scanning. The object was likely placed above the abdomen to provide spiritual protection at the evisceration site. The XRD findings reveal that inclusion F is made of calcite, which is not common in mummies. This is especially interesting because, based on the attenuation of the object alone, it might have been concluded that it was composed of garnet or malachite rather than calcite.
The nondestructive nature of XRD experiments allows researchers to shed new light on various preserved objects without the need for unwrapping them, and it is a method that has a promising future in advancing humankind’s rich knowledge of history.