Makrana marble, famed for its use in the Taj Mahal, Dilwara Temple, and Jaswant Thada, is renowned for its pristine white color, strength, and resistance to seepage. Yet, exposure to extreme temperatures, rain, wind, and increasing pollution continues to degrade this heritage stone over centuries. Accurate assessment of damage is critical for restoration and preservation efforts.
Researchers from the Indian Institute of Technology Bombay, Ms Anupama Ghimire and Prof Swathy Manohar, have developed laboratory methods to simulate natural weathering in Makrana marble, providing a scientific basis for restoration strategies. Their study, published in npj Heritage Science, introduces protocols to reproduce porosity levels in lab samples that match those of field-weathered marble.
To evaluate marble integrity, the researchers relied on Ultrasonic Pulse Velocity (UPV) testing, a non-destructive testing (NDT) method. UPV measures the velocity of ultrasonic waves passing through the marble; reductions in wave speed indicate degradation. Ghimire and Manohar established a correlation between open porosity—a measure of marble degradation—and UPV, enabling conservators to estimate marble damage without removing material.
“Given that freshly quarried Makrana marble has very low porosity, understanding how thermal weathering affects this property is critical for assessing and mitigating damage in heritage structures,” said the researchers.
The team conducted controlled thermal cycling experiments, heating 5 cm marble cubes at temperatures ranging from 100°C to 400°C, followed by rapid cooling in deionised water. They monitored changes in open porosity, visual appearance, microstructure via Focused Ion Beam-Scanning Electron Microscopy (FIB-SEM), chemical composition using Energy Dispersive Spectroscopy (EDS), and UPV values. They observed that five to seven cycles optimally reproduced the porosity of naturally weathered marble.
Prof Manohar highlighted the importance of correlating NDT results with material degradation: “Because each stone type behaves differently, NDT values alone do not indicate damage unless such correlations are established. Correlated NDT datasets are limited for materials such as bricks and stones, but are available for conventional materials in modern construction, such as concrete.”
The research also generated an equation mapping UPV measurements to open porosity, allowing heritage professionals to quickly assess the condition of Makrana marble in situ. While the method is highly effective for moderately degraded marble, the researchers note that UPV reliability diminishes once open porosity exceeds certain thresholds.
“The study also opens possibilities such as defining threshold UPV values that indicate when intervention is needed, developing predictive models for long-term deterioration, creating deterioration maps of heritage structures using portable UPV tools, and integrating NDT-driven data into 3D digital twins for continuous heritage monitoring. This work therefore supports future digital, science-based conservation practices,” Prof Manohar added.
By combining laboratory simulations of thermal weathering with advanced NDT techniques, this study equips conservationists with practical tools to monitor and preserve India’s iconic Makrana marble heritage, ensuring structural stability and aesthetic integrity for future generations.
