How Multimodal Spectroscopy Diagnosed Salt Damage in Valencia’s Renaissance Vaults

The preservation of historical paintings and artifacts helps societies recognize and honor the contributions of those who came before. Ensuring these artifacts are well-preserved helps establish a historical record that previous generations can trace, allowing them to learn more about their own history.

That is why many researchers, including analytical scientists, are exploring new and improved ways to preserve historical artifacts, paintings, and murals. A recent investigation conducted by researchers at the University of the Basque Country UPV/EHU in Spain examined the mural paintings that were in the vault of the Valencia Cathedral, in Valencia, Spain. The findings of their study, which were published in the journal Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, demonstrate how advanced, non-invasive analytical chemistry can revolutionize the conservation of large-scale heritage artworks (1).

Read More: Spectroscopy Guides Long-Term Conservation of Renaissance Murals in Valencia

The Valencia Cathedral is perhaps one of the best well-known Catholic churches in western Europe. Located in Valencia, Spain, the Valencia Cathedral houses the Holy Grail, traditionally believed to be the chalice used by Jesus at the Last Supper (2). Apart from its historical value, the Cathedral is also known for its architecture. The exterior and interior of the Cathedral contains elements of Romanesque, Renaissance, Gothic, and Baroque architectural styles (2).

Inside the church, the Valencia Cathedral also houses an assortment of artwork that is culturally and historically significant. In 2004, an art restoration team discovered some ancient murals tucked beneath the Baroque vaulting (1,3). Known as the Angel Musicians murals, they are considered to be among the earliest examples of Renaissance painting in Europe (1).

Their rediscovery was hailed as a landmark event in Spanish art history, and the extensive restoration that followed aimed to ensure their long-term preservation (3). Yet only a decade later, new problems emerged: salt efflorescence, polychrome lifting, and surface crusts began to appear, threatening once again the integrity of these murals (1).

After a decade of discovering these murals, scientists were now faced with growing challenges. Therefore, a new restoration plan was enacted, with the hope of saving these works of art from being lost to history. Cathedral authorities initiated a new restoration plan, culminating in a multidisciplinary conservation project launched in 2019 (1). Central to this effort was the research group IBeA, whose mandate was to diagnose the cause of the salts, quantify impact, and develop a scientifically informed plan to achieve durable conservation results, which is something the 2004 intervention had failed to secure (1).

Ultimately, this effort led to a multidisciplinary and complex analytical chemistry study, where numerous analytical strategies, such as in situ spectroscopy, hyperspectral imaging (HSI), laboratory analysis, and multivariate data modeling, were used to analyze the murals, assess the damage to them, and streamline conservation efforts. Using multiple analytical approaches was vital to this study because of the scale of these murals (1). As a result, traditional spot analyses alone were determined to not be sufficient. Instead, the research team devised a multianalytical workflow that brought together portable Raman spectroscopy for point-specific measurements and hyperspectral imaging for broad-area coverage (1).

Not only did the team successfully map the distribution of damaging salts across the vault, but they also identified their chemical origins, mapped their infiltration depths, and revealed a likely centuries-old source of contamination: water infiltration carrying nitrate-rich residues from pigeons that had long inhabited the cathedral roof.

References

1. Etxebarria, I.; Vazquez de la Fuentes, I.; Huidobro, J.; Constantini, I.; et al. Advanced Analytical Solutions for Large-scale Works of Art: Revealing Damage in the Renaissance Wall Paintings of Valencia Cathedral (Spain). Spectrochimica Acta Part A: Mol. Biomol. Spectrosc. 2025, 346, 126846. DOI: 10.1016/j.saa.2025.126846
2. Visit Valencia, Cathedral and Holy Grail. Visit Valencia. Available at: https://www.visitvalencia.com/en/what-to-do-valencia/valencian-culture/monuments-in-valencia/catedral-valencia-cathedral (accessed 2025-12-05).
3. The Associated Press, Hidden fresco found after 300 years. NBC News. Available at: https://www.nbcnews.com/id/wbna5288480 (accessed 2025-12-05).