A High-resolution Ground-Penetrating Radar Framework for Detecting Subsurface Discontinuities in Historic Wall Paintings: A Case Study of Giotto's Mural Paintings

The conservation of ancient architectural heritage remains a fundamental and persistent challenge in cultural heritage management. Wall paintings constitute a significant component of this heritage, representing early and highly valuable forms of artistic expression, particularly within religious and historical buildings from major historical periods such as the Renaissance. Among these works, the mural paintings attributed to Giotto, the founder of modern Western painting and one of the most influential figures in Italian art history, are of outstanding cultural and historical significance.

With the passage of time, wall paintings are increasingly affected by physical and environmental degradation, making their systematic assessment and preservation a critical priority. The identification and characterization of subsurface deterioration within masonry walls and wall paintings, structures that are inherently fragile and multilayered, require the application of reliable non-destructive testing (NDT) techniques. Such deterioration may manifest as subsurface moisture accumulation, voids, or delamination between layers, often induced by environmental factors such as diurnal and seasonal temperature fluctuations, humidity variations, and anthropogenic influences.

Recent advancements in NDT technologies have enabled more detailed investigation of the internal structure of heritage materials.  Among these techniques, Ground Penetrating Radar (GPR) has emerged as a particularly effective tool due to its rapid data acquisition, cost-effectiveness compared to destructive methods, portability, and suitability for non-invasive time-lapse monitoring, as well as its capability to provide high-resolution two-dimensional and three-dimensional imaging of subsurface features. Despite its potential, the application of GPR to wall paintings remains limited, primarily due to challenges associated with data processing and interpretation in complex, thin-layered media [1, 2].

This study aims to address these limitations by developing and applying advanced GPR processing and interpretation strategies for improving the detection and characterization of subsurface defects and material heterogeneities within wall paintings. Considering the limited thickness of the plaster and painted layers, a 2 GHz GPR system with crossed polarized antennas was employed to maximize spatial resolution. Although the high operating frequency restricts penetration depth, it enables detailed imaging of near-surface features that are critical for the diagnostic assessment of wall paintings.

Keywords: Ground Penetrating Radar; Cultural Heritage; Wall Paintings; Non-Destructive Testing; Giotto

Acknowledgement: The authors would like to acknowledge the fruitful visiting scholar exchange between the University of West London (UWL) Faringdon Centre and the University of Florence, which significantly contributed to the successful completion of this study. Additionally, the authors would like to thank Dr. Maria Rosa Lanfranchi (OPD), the restorer, for the contribution to this work.

References

1. Napoli, A. F., Marchetti, E., Coli, M., Ciuffreda, A. L., Morandi, D., Papeschi, P., and Agostini, B.: Application of Ground Penetrating Radar (GPR) analysis on San Giovanni's Baptistery in Florence, EGU 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12917, https://doi.org/10.5194/egusphere-egu24-12917.

2. Ortega-Ramirez, M. Bano, L. A. Villa Alvarado, D. Medellin Martinez, R. Rivero-Chong, C. L. Motolinia-Temol, High-resolution 3D GPR applied in the diagnostic of the detachment and cracks in pre-Hispanic mural paintings at “Templo Rojo,” Cacaxtla, Tlaxcala, Mexico. Journal of Cultural Heritage 50 (2021) 61-72, doi:https://doi.org/10.1016/j.culher.2021.06.008.