Using XRF, XRD, FT-IR, and Confocal Microscopy to Characterize Late Period Egyptian Wooden Sculptures

A recent study published in the journal Polymers provides one of the most comprehensive material characterizations to date of a Late Period Egyptian polychrome wooden sculpture, offering conservators and heritage scientists new baseline data and a minimally invasive analytical framework for similar artifacts.¹ This study, which was led by Dina M. Atwa of Beni-Suef University, investigated a 26th Dynasty Ptah–Sokar–Osiris statuette excavated back in 2020 from the Tari cemetery in the Giza Pyramids area. Collaborating with researchers from Cairo and Riyadh research institutions, the team utilized several spectroscopic and analytical techniques to learn more about the manufacturing choices ancient Egyptians made back in the 26^th Dynasty while assessing the object’s conservation status. The techniques used in this study include X-ray fluorescence (XRF), synchrotron-based X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and confocal microscopy.¹

The 26^th Dynasty of Ancient Egypt was known as the Saite Period. It was known as the last great native dynasty of ancient Egypt before the Persians conquered them.² The 26^th Dynasty lasted approximately 130 years, and while concerns grew about its sustainability, there were numerous strides made in artistic expression, which can be seen in the stone monuments and sculptures left behind.²

In their study, the research team examined one of these sculptures that represented the funerary deity Ptah–Sokar–Osiris, which is a composite god associated with regeneration and the afterlife.^1,3 The object’s secure archaeological context and variable preservation state made it a suitable case study for investigating workshop practices and degradation mechanisms in Late Period polychrome wooden artifacts.¹

How did the researchers apply spectroscopic techniques?

For establishing the cellulose crystallinity index, the researchers use synchrotron XRD analysis. The XRD analysis revealed that the sculpture had moderate structural preservation of the wood. Then, the researchers evaluated its chemical composition using FT-IR spectroscopy. Here, they discovered that substantial chemical deterioration had taken place. A carbonyl index of 2.22 and the loss of amorphous cellulose and hemicellulose pointed to extensive lignin oxidation and polymer breakdown.¹ The combined techniques provided complementary insights into both the structural integrity and chemical damage.

The researchers also looked at pigment identification. They documented carbon black applied over a calcite-based ground layer; Egyptian Blue (cuprorivaite) at 55 ± 5 wt %; green layers originally based on malachite (now only 10 ± 2 wt %); orpiment at 60 ± 5 wt %; red ochre dominated by hematite at 69 ± 5 wt %; and a high-purity calcite preparation layer (93 ± 2 wt %) with minor gypsum.¹ Metallic gold, measured at 40 ± 5 wt %, confirmed the object’s elite status.¹

A key insight from this study was that burial practices led to sculptures having their pigments altered. The researchers concluded this when they observed the predominance of atacamite (65 ± 5 wt %) in green areas is interpreted as a secondary transformation product formed through chloride-mediated alteration of original malachite over approximately 2,600 years.¹ The identification of atacamite as a diagenetic phase rather than an original pigment helped the researchers answer long-standing questions about green copper-based pigments in Egyptian artifacts.

And finally, confocal microscopy was used by the team to learn about the pigment-mixing strategies used in ancient Egypt. The consistent detection of calcite, which was typically 20–45%, across colored layers confirms the standardized use of ground layers in 26th Dynasty Lower Egyptian workshops.¹ These findings contribute to the debate over whether Saite artistic archaism reflected mere stylistic revival or technical continuity.

The study also addressed binding media. The FT-IR spectra showed weak organic signals and an absence of protein amide bands, which are patterns consistent with a carbohydrate-based binder such as plant gum.¹ However, the authors caution that degraded matrices and non-specific signals limit definitive identification without more sensitive, and destructive, methods such as gas chromatography–mass spectrometry (GC–MS).¹ This highlights both the promise and limitations of non-destructive or minimally invasive techniques.

From a conservation perspective, the findings indicate the need for specialized consolidants, stabilization of paint layers, and controlled environmental storage conditions to preserve ancient wooden sculptures. Without intervention, further deterioration is likely.

References

1. Atwa, D. M.; Hussein, R. K.; Mohamed, I. F. et al. Structural and Chemical Degradation of Archeological Wood: Synchrotron XRD and FTIR Analysis of a 26th Dynasty Egyptian Polychrome Wood Statuette. Polymers 2026, 18 (2), 258. DOI: 10.3390/polym18020258
2. The Metropolitan Museum of Art, Egypt in the Late Period (ca. 664–332 B.C.). Met Museum. Available at: https://www.metmuseum.org/essays/egypt-in-the-late-period-ca-712-332-b-c (accessed 2026-03-03).
3. The Metropolitan Museum of Art, Figure of Ptah-Sokar-Osiris. Met Museum. Available at: https://www.metmuseum.org/art/collection/search/551504 (accessed 2026-03-03).