Possible antimicrobial activity of Egyptian blue in Roman nymphaea and fountains

Egyptian Blue (EB), the earliest synthetic pigment developed in antiquity, has been extensively studied for its structure, manufacture, applications and unique near-infrared luminescence. While its widespread use as a pigment in wall paintings and ceramics is well documented, its application as solid mosaic tesserae, particularly in Roman water-related architecture, has received far less attention. This interdisciplinary study investigates whether the deliberate selection of EB in water-related architectural contexts may have extended beyond canonical considerations. It combines archeological observations with laboratory microbiological experiments to investigate whether the selection of EB in Roman water features may have been influenced by its ability to inhibit biological colonization. Visible-Induced Luminescence (VIL) imaging confirmed the systematic presence of EB tesserae in Roman water features examined, while experimental tests showed that EB exhibits broad antialgal activity and selective antimycotic properties, with a complete inhibition for only one Aspergillus strain. Our results provide an experimental support for the hypothesis that EB may have fulfilled a dual role in Roman nymphaea and fountains, serving not only as a decorative material but also as a functional surface capable of limiting biological colonization in humid environments. This study offers a new perspective on the technological knowledge underlying the selection of materials in Roman architectural decoration.