Technology and Composition of the Mortar and Origin of the Stone and the Smalta Tesserae of the Early Christian Mosaics from Parthicopolis. The Beginning of Database on the Ancient Mosaics from Middle Strymon

The article presents the results of a study on the mortar and tesserae made of marble, sandstone, brick, and smalta in the mosaic pavement of the exonarthex of Basilica No. 2 in Parthicopolis. This basilica served as an important episcopal center in the province of Macedonia I. The methods employed include macro- and micro-analysis, as well as SEM-EDS and XRD analysis of the mineral phases. It has been established that the mosaic was laid on a mortar layer without a statumen and rudus. The study of the mortar revealed the presence of a fine fraction among the tesserae, as well as lumps of lime in the mortar composition, which were reinforced with a fine brick powder. The brick and stone tesserae, including marble and sandstone, originated locally, while the smalta used for the glass tesserae was imported, possibly undergoing secondary processing on-site. The analysis of the smalta composition identified several technological processes, including secondary heating, a significant presence of small air bubbles, and unwanted crystalline impurities. These phenomena likely occurred during the melting, molding, annealing, or secondary processing of sodium-lime-silicate glass. This suggests the possibility of imported manufactured production being remade in situ, demonstrating the utilization of local materials and techniques. The study revealed that the mosaicists possessed a profound understanding of the craft, including a deep knowledge of the underlying processes and a diverse range of technical skills. With this expertise, they were able to successfully achieve the desired result by utilizing local materials.