Micro-Raman spectroscopy THz time domain spectroscopic imaging of ‘Pietra Dura’ Marble inlay work resembling Taj Mahal architectural motifs

摘要

The Taj Mahal, a 17th century architectural wonder is known worldwide for its visual appeal in white marble with beautifulinlay works in the style of ‘Pietra Dura’ from Florence, Italy. The long-drawn restoration process for structural damageand surface discoloration of this heritage structure has drawn international attention. The conventional means of structuralsurvey is based mostly on visual assessments by experts which is highly time-consuming and subjective; and in most casescan be done only after the damages become apparent. Consequently, the restoration involves exhaustive repair procedures.In this work, we have introduced a combination of optical imaging and spectroscopy techniques, namely, μ-RamanSpectroscopy and Terahertz Time Domain Spectroscopic Imaging, as an alternative approach for both surface and subsurfacedamage detection in Marble structures. In our work, we have examined some of the most common structural andsurface damages in heritage Marble architectures found worldwide using some selected representative models. Thesemodel slabs bearing similar ornamental colourful motifs like those in the Taj Mahal were probed by the above twotechniques, which showed tremendous promise in sensing very fine cracks which are visually impossible to detect. Also,minute changes in surface quality due to the introduction of organic materials were mapped with high accuracy. This pavesthe way for an efficient and trusted survey platform that could be deployed in future which would be able to provide a fastand reliable structural assessment of our cultural heritage architectures for the next generation.