Some of the most celebrated frescoes at the ancient Roman site of Pompeii have been given a clean bill of health, thanks to a course of antibiotics. Conservators used amoxicillin, a type of penicillin, to treat strains of bacteria living in the Dionysiac frieze that decorates what scholars believe to be the dining room of the Villa of the Mysteries. The streptococcus bacteria were thriving on the paintings’ natural pigments and turning them to powder. The house reopened to the public in March after an extensive, two-year restoration project.

Under the supervision of Stefano Vanacore, the head of Pompeii’s restoration laboratory, a team of 20 people from the private firm Atramentum gave the villa a thorough makeover. They also removed traces of soil in the paintings that had been left over from the excavation of the site in the early 1900s. Beginning in 2013, the team spent more than a year stabilising the mosaic floors and cleaning thousands of square metres of interior decoration across the house.

Analysis revealed the wide range of painting techniques used on the walls, from encaustic (paint mixed with melted wax) and water-based pigments to the rare compound “Egyptian blue”.

Particular attention was paid to the deep red colour used so extensively in the frieze. Conservators used lasers to remove dark stains that had formed in the pigment (made from the mineral cinnabar) over time as soil particles containing the black mineral manganese became soluble in rainwater, which seeped through cracks in the ancient masonry.

The restoration of the frescoes completes the second phase of work on the Villa of the Mysteries, following interventions, which began in 2008, to reinforce the structure and to renovate roofing measuring more than 2,500 sq. m. Further work will be required on a part of the site that closed in September 2012 after a supporting beam collapsed during a heavy rainstorm.