Mosaics are one of the most important decorative elements of Roman culture. They were built with small pieces called tiles. Sometimes these pieces were made of marble or another type of colored stone, which was cut into fine cubes. In others, they were manufactured with a calcium carbonate base and then covered with a pictorial layer.
The tiles were then joined with silt or other binders to form geometric or figurative motifs.
Now, researchers from the University of the Basque Country (UPV / EHU), the University of Valladolid (UVa) and the Pompeii Archaeological Park (Italy) have carried out a study, published in the journal Heritage Science, which reveals the elaboration technique and the composition of the mosaics from the House of the Golden Cupids in the ancient Roman city of Pompeii.
The objective of the work was twofold: on the one hand, to determine what elaboration technique are these mosaics and, on the other, know its state of conservation: what are the deterioration processes they are suffering and what corrective measures can be put in place.
As Juan Manuel Madariaga, head of the research team, explains, "identifying both the substrate of the tiles and the compounds with which they are colored is a challenge for chemists and archaeologists."
Analysis 'in situ'
To perform the mineralogical characterization, they analyzed the tiles in situ using non-destructive spectroscopy and spectrometry techniques, and used LIBS spectroscopy to perform elemental analysis.
The results indicate that in the House of the Golden Cupids both types of techniques were used to make tesserae "Pieces of natural rock and pieces of manufacture, a body with a carbonate base and a pictorial layer that determines the color of the mosaic."
The white tesserae were composed mainly of calcite, while local volcanic rocks were used to make the black tiles. Likewise, the red ones were composed of a calcite matrix with a pictorial layer of hematite, while the oranges were obtained by diluting hematite in the calcite matrix.
In relation to the state of conservation of these mosaics, Madariaga points out that, due to the chemical nature of the tesserae, "they are the least damaged decorative elements within Pompeii."
In them, he adds, “the deterioration processes that we have observed on the walls and in the wall paintings are not so evident. Thus, it would only be necessary that no water with dissolved ions reached them since, when these ions dry, they precipitate and form normally white patina that change the appearance of the mosaic ”.
In addition, Madariaga points out that still there are outdoor mosaics in the city and that a simple action to protect them would be "to install roofs that were not of the term type (uralitas, plastics) to avoid water infiltration".
The team started working in Pompeii 10 years ago. "We have recently renewed the agreement with the Pompeii Archaeological Park for three more years," says Madariaga, who underlines that, in addition to purely scientific works, "it is about disseminating and disseminating the results, for example showing in museums work, letting tourists see in situ how we investigate and telling them what we do ”.
Marcaida, I., Maguregui, M., Morillas, H., Prieto-Taboada, N., Veneranda, M., de Vallejuelo, S. F. O.,… & Madariaga, J. M. (2019). "In situ non-invasive multianalytical methodology to characterize mosaic tesserae from the House of Gilded Cupids, Pompeii". Heritage Science, 7 (1), 3.