A new chemical study of the splendid wall paintings of the Domus of Salvius in present-day Cartagena has uncovered a previously unknown ancient recipe for stretching expensive pigment without sacrificing quality.
In its ancient heyday, cinnabar was called "red gold," and it was one of the most sought-after minerals of the time. Using a variety of analytical techniques, a multidisciplinary team found a paint mixture previously undocumented in Hispania. It demonstrated an ingenious understanding of chemistry that enabled painters to get the most out of this expensive material.
The discovery brings the art down to earth: making pigment cost money 2,000 years ago, just as it does today. The ancient craftspeople had figured out how to use cinnabar sparingly. Rather than reflecting the affluent family's budget, mixing iron oxide and cinnabar appears to have been a common practice. The method also included a primer.
It was not the mixture itself that struck the study's authors, but the material applied to the walls beforehand. This revealed another technique the painters used to ensure the durability of cinnabar's red color. Researchers even suspect that this knowledge may have spread through books or workshops.
A Sophisticated Way of Painting
For the study, chemists from the Chemical Institute for Energy and Environment at the University of Cordoba teamed up with researchers from the University of Murcia.
The wall paintings of Carthago Nova had been extensively studied because the city was one of the most notable in the region. Yet their chemical composition had not been examined, leaving unanswered questions about how the works of art in Room 3 of the Domus of Salvius were made.
According to the study in npj Heritage Science, X-ray diffraction analysis of the mortars confirmed the use of locally sourced materials. Analysis using Raman spectroscopy and scanning electron microscopy identified the painting techniques and chromatic palette, highlighting the use of cinnabar.
Making a Little Go a Long Way
Because cinnabar was costly, the client had to purchase and supply it. Researchers explained that iron oxide was commonly mixed with the more expensive material because both produced the desired red hue.
What astonished the researchers was the primer laid on the wall: yellow goethite had been applied first. This showed that the painters had a sophisticated understanding of the chemistry needed to protect the cinnabar, lime, and iron oxide, helping the cinnabar last longer and retain its appearance.
The study also extended the known timeline for the use of cinnabar. Archaeologists had believed the pigment had fallen out of use, but the date of the walls challenged that view. Findings from paintings at Ephesus supported the research, suggesting that a family of recipes existed for applying cinnabar over large surfaces.