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Image Credit: Carole Raddato, CC BY-SA 2.0, via Wikimedia Commons
Roman Mosaics in Spain Made from Recycled Mining Waste, Study Finds
A new study has revealed that black tesserae used in Roman mosaics from southern Spain were produced using recycled metallurgical waste derived from ancient lead and silver smelting activities. The research provides rare direct evidence for the reuse of industrial by-products in Roman decorative art.
The study examined black vitreous tesserae from mosaics dated between the late 1st and 5th centuries AD at three archaeological sites in the Upper Guadalquivir region: Cástulo, El Altillo, and Cerrillo del Cuco. All of these sites are located within the historic Linares–La Carolina mining district, one of the most important Roman lead- and silver-producing regions in Hispania.
Researchers used Raman spectroscopy, micro X-ray fluorescence, and lead isotope analysis to compare the tesserae with local metallurgical slags recovered from ancient mining areas. The analyses demonstrated that the mosaic materials consist of lead–silicate glass with exceptionally high lead concentrations and chemical signatures closely matching local smelting waste.
According to the study, the black tesserae differ significantly from conventional Roman glass. Most Roman mosaic glass was produced using soda–lime–silica compositions fluxed with natron, but the tesserae examined here contain unusually high levels of lead and almost no sodium, indicating a different technological origin.
The research identified additional evidence linking the tesserae to metallurgical processes, including traces of amorphous carbon associated with charcoal-fuelled smelting, quartz and cristobalite inclusions formed under high temperatures, and metallic lead residues preserved within the glassy matrix.
The mosaics themselves decorated both urban and rural elite contexts. Among them is the famous (Mosaic of Los Amores) from Cástulo, which includes mythological scenes such as the Judgment of Paris and Selene with Endymion.
Researchers suggest that the proximity between mining centers, smelting workshops, and mosaic production sites made the reuse of slag particularly practical. Rather than being discarded, vitreous waste from lead production appears to have been deliberately selected, modified, and integrated into architectural decoration.
The study concludes that Roman workshops in the region developed an efficient system of material reuse that linked extractive industries with artistic production, highlighting a sophisticated form of resource management within the Roman economy.
Published on: 17-05-2026
Edited by: Abdulmnam Samakie
Source: npj Heritage Science
