An Uncommon Instance of Egyptian Blue in the “Pigmented Intonachino” of the Fishpond Wall Painting From the Roman Villa of Torre di Pordenone (Northeast Italy)

The increasingly close integration of analytical techniques in the study of Greek and Roman wall paintings has shown that Egyptian blue was a common pigment, widely documented in the production of blue and greenish hues in ancient painted production. This study reports on a peculiar use of this synthetic pigment identified in wall-painting fragments recovered from secondary deposits at the Roman villa of “Torre di Pordenone” (Friuli-Venezia- Giulia, northeast Italy). The site yielded numerous finely executed fragments with marine-themed motifs, interpreted as part of a painted fishpond. These remains, dated between late 1st c. CE and the first half of the 2nd c. ce according to stylistic features, contribute to the reconstruction of the villa's exceptionally rich decorative program. A distinctive feature is the uncommon use of raw materials in both the preparation mortars and painted layers. Transmitted polarized light optical microscopy (TPL–OM), combined with scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM–EDS), was used for the petro-mineralogical and microchemical characterization of the mortars. Reflected light optical microscopy (RL-OM), X-ray powder diffraction (XRPD), SEM–EDS, micro-Raman, and micro-X- Ray Fluorescence (micro-XRF) analyses revealed traces of Egyptian blue both on the surface and within the intonachino layer, with coarse cuprorivaite grains detected up to 3.0 mm below the surface. This distribution is not compatible with the penetration of pigments in fresco painting but indicates the deliberate mixing of Egyptian blue with lime, consistent with the practice of the “pigmented mortar,” used to obtain homogeneous, pale blue tones for the marine background. Therefore, this case represents a rare example of Roman “blue lime-painted mortar,” more commonly achieved with ochre pigments, and prompts renewed discussion on the availability of Egyptian blue in Roman markets, thus contributing to a more nuanced understanding of its distribution, accessibility, and technological standardization within Roman material culture.