Spectroscopic Investigation of Wall Paintings in the Alhambra Monumental Ensemble: Decorations with Red Bricks

A spectroscopic investigation of the Alhambra Monumental Ensemble in Granada, Spain, reveals that the red brick-like decorations—found across exterior and interior walls, arches, and vaults—were primarily created using hematite (α-Fe₂O₃) as the pigment, likely derived from natural red ochre abundant in the region. The study, combining non-invasive techniques like X-ray fluorescence (XRF) and Raman spectroscopy with lab-based analyses such as SEM-EDS and Raman microimaging, found that these decorations were typically applied over a white lime mortar base, suggesting traditional fresco or mezzo fresco techniques. However, one indoor location used gypsum plaster, with calcium oxalate (weddellite) detected as a result of organic binder degradation. Outdoor decorations showed significant superficial contamination with gypsum, contrasting with better-preserved interior motifs.

Arjonilla, P., Ayora-Cañada, M., de la Torre-López, M., Correa Gómez, E., Rubio Domene, R., & Domínguez-Vidal, A. (2021). Spectroscopic Investigation of Wall Paintings in the Alhambra Monumental Ensemble: Decorations with Red Bricks. Crystals, 11(4), 423. https://doi.org/10.3390/cryst11040423