A new chemical study of the splendid wall paintings of the Domus of Salvius in present-day Cartagena discovered a previously unknown ancient recipe for mixing paint that didn’t sacrifice quality for cost.

In its ancient heyday, cinnabar was called “red gold,” one of the most sought-after minerals of the time. A multidisciplinary study, using a variety of analytical techniques, revealed a never-before-seen paint mixture in Hispania that demonstrated an ingenious understanding of chemistry, enabling these housepainters to get the most out of this expensive material.

The team behind the extraordinary discovery brought art “down the earth,” as it cost money 2,000 years ago, as it would today, to make pigment. In this case, these ancient craftsmen figured out how to sparingly use Cinnabar, which spoke less to the affluent family’s budget, but rather a common practice to mix iron oxide and cinnabar that included a primer.

It wasn’t the mixture itself that struck these study authors, but rather the material they applied to the walls beforehand, thereby finding another technique they used to ensure the durability of the red color of cinnabar. Researchers went as far as to suspect that this knowledge might have spread in books or workshops.  

A sophisticated way of painting

For the study, chemists from the Department of Organic Chemistry at the Chemical Institute for Energy and Environment at the University of Córdoba (IQUEMA) teamed up with researchers from the Department of Prehistory, Archaeology, Ancient History, Medieval History, and Historiographical Sciences and Techniques at the University of Murcia.

These pioneering chemists from IQUEMA also spearheaded other astonishing, detailed archaeological initiatives that determined the compositions of old wine and aromas of the Roman Empire and of the mortars used in the Domus of Salvius, in the present case.

Although the wall paintings of Carthago Nova had been extensively studied, as one of the most notable cities in the Hispanic region of the Roman Empire, their chemical composition hadn’t been examined, perhaps with knowledge to share about how these splendid works of art were made in Room 3 of the famous Domus of Salvius.

X-ray diffraction (XRD) analysis of the mortars confirmed the use of locally sourced materials, according to the study in npj Heritage Science. Pigment analysis with Raman spectroscopy and scanning electron microscopy (SEM) identified the painting techniques and the chromatic palette, highlighting the use of cinnabar, as per the study.

Making a little go a long way

As cinnabar was costly, the client had to purchase and supply it. Researchers explained that iron oxide was commonly mixed with this more expensive material as they both achieved the desired red hue.

It was the primer that had been laid on the wall that astonished these researchers, as yellow goethite had been applied first. It showed that ancient Roman craftsmen had a sophisticated understanding of the chemistry that would protect the cinnabar, lime, and iron oxide, so the cinnabar would last longer and retain its appearance, as per Phys.

The study has extended the known chronology of the use of cinnabar, as archaeologists believed it had fallen out of use, but the date of the walls challenged that timeline. The methods employed here were called “a novelty in a Spanish context.” The recent findings on the paintings of Ephesus supported this research, indicating the existence of a kind of ‘family of recipes’ for the application of cinnabar on large surfaces, the study concludes.

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