Abstract
Abstract. Raman spectroscopy has been applied to check if there are detectible material differences beneath the inscribed and non-inscribed areas of marble-based written artefacts, which could be further used to visualize lost or hardly readable text via suitable mapping. As a case study, marble segments with ∼ 2000-year-old inscribed letters from Asia Minor (western Turkey) and marble gravestones with 66 ± 14-year-old inscriptions from the cemetery of Ohlsdorf (Hamburg, Germany) have been subjected to Raman spectroscopy, as well as to complementary X-ray diffraction, wavelength-dispersive electron probe microanalysis, and Fourier-transform infrared spectroscopy, to thoroughly study the effect of different environmental conditions, grain size, and inscription age on the nature and penetration depth of marble alteration. The results demonstrate that environmental conditions rule over the type of dominant weathering changes, which are carotenoid molecular inclusions produced by lichen and amorphous carbon for marbles from Hamburg and Asia Minor, respectively. The alteration is much stronger in medium- and coarse-grained than in fine-grained marble, but it is suppressed by letter colouring. In the absence of letter colouring, the weathering-related products in both ancient and modern engraved marbles are more abundant beneath than away from the engraved areas, and the penetration depth is larger due to the enhancement of fissures and micro-cracks around the inscribed areas. We show that the Raman intensity ratio between the strongest peak of the weathering-related product (ν(C=C) ∼ 1520 cm−1 for carotenoids or the G peak ∼ 1595 cm−1 for soot-like carbon) and the strongest peak of marble (CO3 stretching near 1087 cm−1) can serve as a quantitative marker to indirectly map the lateral distribution of cracks induced during the inscribing process and hence can potentially be used to trace lost text on vanished marble inscriptions. This approach can be applied to other rock types, but further studies are required to identify the corresponding autochthonous weathering-related products.
Highlights
Mineralogical analyses of rock-based writing supports are crucial to understand the roots of human civilization since the written language, as a communicational expression, is the most widespread and secure practice of transmitting knowledge through time
The results demonstrate that environmental conditions rule over the type of dominant weathering changes, which are carotenoid molecular inclusions produced by lichen and amorphous carbon for marbles from Hamburg and Asia Minor, respectively
We show that the Raman intensity ratio between the strongest peak of the weathering-related product (ν(C=C) ∼ 1520 cm−1 for carotenoids or the G peak ∼ 1595 cm−1 for soot-like carbon) and the strongest peak of marble (CO3 stretching near 1087 cm−1) can serve as a quantitative marker to indirectly map the lateral distribution of cracks induced during the inscribing process and can potentially be used to trace lost text on vanished marble inscriptions
Summary
Mineralogical analyses of rock-based writing supports are crucial to understand the roots of human civilization since the written language, as a communicational expression, is the most widespread and secure practice of transmitting knowledge through time. Inscribed rocks have been thought to be the most persistent medium in time, and they were introduced in the form of rectangular mould-based bricks in Mesopotamia at least from the 4th or 3rd millennium BCE (Artioli, 2010, and references therein). In ancient Greece and Rome, marble, limestone, and granodiorite became the common writing supports in the 1st millennium BCE. S. Aspiotis et al.: Crack-enhanced weathering in inscribed marble layers and limited visibility of the inscribed text. Since many ancient inscriptions are not visible anymore or virtually unreadable, much effort has been put in finding methods which might unravel the epigraphic content of stone objects
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