Synchrotron XRF spectroscopy for reading salt-encrusted cuneiform tablets

Abstract

Cuneiform tablets were a primary writing medium in the ancient Near East from the late fourth millennium BCE to the first century CE. Although these clay tablets were durable for daily use, prolonged burial over millennia has made them vulnerable to salt damage. Fluctuations in temperature and humidity cause the migration of salts to the surface of the tablets, damaging them and covering the inscriptions, making the text unreadable. Traditional preservation and restoration techniques, such as firing and tetraethyl orthosilicate (TEOS) treatments, although effective in making the text legible again, cause irreversible physicochemical alterations, compromising the historical integrity of the tablets. To address this issue, we used synchrotron radiation X-ray fluorescence (SR-XRF) spectroscopy to analyze cuneiform tablets covered by salts. This method enabled the recovery of previously unreadable texts without altering the nature of the tablets. Our findings highlight the importance of non-invasive methods for preserving and studying cuneiform tablets, maintaining their physicochemical integrity, and allowing for future analyses.

Fig. 1

Confocal XRF spectra obtained from different points on tablet LW21.CUN.47, showcasing the elemental variations between salt-covered clay, salt-free surface clay, and sub-surface clay (30 μm beneath the surface). Each point was measured for 600s.

Fig. 2

Close-up of the 1–7 keV region of Fig. 1 to allow for better comparison of the low-Z element composition of salt-covered clay, salt-free surface clay, and sub-surface clay (30 μm beneath the surface). Each point was measured using confocal XRF for 600s.

Fig. 3

X-ray transmission efficiency of different characteristic XRF lines or an arbitrary energy of 30 keV, as a function of salt layer thickness. The salt composition is derived from Table 1, completed with CO₃ to obtain 100 w%.

Fig. 4

Analysis of cuneiform tablet LW21.CUN.70 using non-confocal imaging techniques and CT Scanning. Left: General view of the cuneiform tablet. Center: Close-up views of two areas (A and B) analyzed with non-confocal imaging. Right: CT scan sections showing the thickness of the salt layer in areas A (0.92 mm) and B (0.63 mm). Measurement conditions: 50 × 50 μm² pixels, 0.3 s/pt.

Fig. 5

Analysis of tablet LW21.CUN.14 using non-confocal imaging techniques. Bottom left: General view of the tablet (reverse) showing a consistent salt layer thickness of 0.5 mm. Top left: Four areas (A-D) analyzed with non-confocal imaging are highlighted in different colors. Right: Close-up views of the areas (A-D) showing salt deposits alongside visualizations with the Rb signal, which markedly enhances the legibility of cuneiform signs covered by the salt. Measurement conditions: 50 × 50 μm² pixels, 0.3 s/pt (A); 0.2 s/pt (B and C); 0.1 s/pt (D).

Fig. 6

Left: General view of the tablet LW21.CUN.14 with the analyzed area highlighted. Right, A: Close-up of the highlighted area showing the presence of salt, which covers some cuneiform signs. Right, B: Close-up of the highlighted area with the addition of the Rb signal, which allows for the reading of the cuneiform signs covered by salt.

Fig. 7

Left: Tablet LW21.CUN.14 mounted on the 3D-printed support. Right: Overview of the sample (LW21.CUN.14) and measurement geometry at the PUMA beamline (SOLEIL, France) displaying the different detector configurations. A: Sample; B: Primary beam; C: Non-confocal detector; D: Confocal detector.