Suzanne's Mom's Blog

How do you clean a masterpiece? Carefully, My Friends. Especially if much of the damage was caused by the decomposing body of a long-dead Medici.

Jason Horowitz reports at the New York Times that you may also want to keep any strange method of cleaning a secret until after it actually succeeds.

“As early as 1595, descriptions of stains and discoloration began to appear in accounts of a sarcophagus in the graceful chapel Michelangelo created as the final resting place of the Medicis. In the ensuing centuries, plasters used to incessantly copy the masterpieces he sculpted atop the tombs left discoloring residues. His ornate white walls dimmed.

“Nearly a decade of restorations removed most of the blemishes, but the grime on the tomb and other stubborn stains required special, and clandestine, attention. … Restorers and scientists quietly unleashed microbes with good taste and an enormous appetite on the marbles, intentionally turning the chapel into a bacterial smorgasbord.

“ ‘It was top secret,’ said Daniela Manna, one of the art restorers. …

“ [A team headed by] Monica Bietti, former director of the Medici Chapel’s Museum … used bacteria that fed on glue, oil and apparently [a dead Medici’s] phosphates as a bioweapon against centuries of stains.

“In November 2019, the museum brought in Italy’s National Research Council, which used infrared spectroscopy that revealed calcite, silicate and other, more organic, remnants on the sculptures and two tombs that face one another across the New Sacristy.

“That provided a key blueprint for Anna Rosa Sprocati, a biologist at the Italian National Agency for New Technologies, to choose the most appropriate bacteria from a collection of nearly 1,000 strains, usually used to break down petroleum in oil spills or to reduce the toxicity of heavy metals. …

“Then the restoration team tested the most promising eight strains behind the altar, on a small rectangle palette spotted with rows of squares like a tiny marble bingo board. All of the ones selected, she said, were nonhazardous and without spores.

“ ‘It’s better for our health,’ said Manna, after crawling out from under the sarcophagus. ‘For the environment, and the works of art.’ …

“In February 2020 Covid hit, closing the museum in March and interrupting the project. … The bacteria strains got back to the Medici Chapel, which had reopened with reduced hours, in mid-October. Wearing white lab coats, blue gloves and anti-Covid surgical masks, Sprocati and the restorers spread gels with the SH7 bacteria — from soil contaminated by heavy metals at a mineral site in Sardinia — on the sullied sarcophagus of Lorenzo di Piero, Duke of Urbino, buried with his assassinated son Alessandro.

“ ‘It ate the whole night,’ said Marina Vincenti, another of the restorers. …

“In 2016, [she had] attended a conference held by Sprocati and her biologists. (‘An introduction to the world of microorganisms,’ Sprocati called it.) They showed how bacteria had cleaned up some resin residues on Baroque masterpiece frescoes in the Carracci Gallery at Palazzo Farnese in Rome. Strains isolated from mine drainage waters in Sardinia eliminated corrosive iron stains in the gallery’s Carrara marble.

“When it came time to clean the Michelangelos, Vincenti pushed for a bacterial assist.

“ ‘I said, “OK,” said [Paola D’Agostino, who runs the Bargello Museums]. ‘ “But let’s do a test first.” ‘

“The bacteria passed the exam and did the job.”

More at the Times, here.