FLORENCE, Italy — As early as 1595, descriptions of stains and discoloration began to appear in accounts of a sarcophagus in the graceful chapel that Michelangelo created as the final resting place of the Medicis. In the ensuing centuries, plasters that were used to incessantly copy the masterpieces he sculpted atop the tombs left discoloring residues. His ornate white walls dimmed.
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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. In the months leading up to Italy’s
COVID-19 epidemic and then in some of the darkest days of its second wave as the virus raged outside, 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.
On a recent morning, she reclined — like
Michelangelo’s allegorical sculptures of Dusk and Dawn above her — and reached into the shadowy nook between the chapel wall and the sarcophagus to point at a dirty black square, a remnant showing just how filthy the marble had become.
She attributed the mess to one Medici in particular, Alessandro Medici, a ruler of Florence, whose assassinated corpse had apparently been buried in the tomb without being properly eviscerated. Over the centuries, he seeped into Michelangelo’s marble, the chapel’s experts said, creating deep stains, button-shaped deformations and, more recently, providing a feast for the chapel’s preferred cleaning product, a bacteria called Serratia ficaria SH7.
“SH7 ate Alessandro,” Monica Bietti, former director of the Medici Chapels Museum, said as she stood in front of the now gleaming tomb, surrounded by Michelangelos, dead Medicis, tourists and an all-woman team of scientists, restorers, and historians. Her team used bacteria that fed on glue, oil, and apparently Alessandro’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. Some of the bugs in her lab ate phosphates and proteins, but also the Carrara marble preferred by Michelangelo.
“We didn’t pick those,” Bietti said.
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.”
Sprocati said they first introduced the bacteria to Michelangelo’s tomb for Giuliano di Lorenzo, Duke of Nemours. That sarcophagus is graced with allegorical sculptures for Day, a hulking, twisted male figure, and Night, a female body Michelangelo made so smooth and polished as to seem as if she shined in moonlight. The team washed her hair with Pseudomonas stutzeri CONC11, a bacteria isolated from the waste of a tannery near Naples, and cleaned residue of casting molds, glue, and oil off her ears with Rhodococcus sp. ZCONT, a strain that came from soil contaminated with diesel in Caserta.
It was a success. But Paola D’Agostino, who runs the Bargello Museums, which oversees the chapels and which will officially reveal the results of the project in June, preferred to play it safe on Night’s face. So did Bietti and Pietro Zander, a Vatican expert who joined them. They allowed the restorers to give her a facial of micro-gel packs of xanthan gum, a stabilizer often found in toothpaste and cosmetics that is derived from the Xanthomonas campestris bacteria. The head of Duke Giuliano, hovering above his tomb, received similar treatment.
Then, in February 2020, COVID hit, closing the museum the next month 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.
When it came time to clean the Michelangelos, Vincenti pushed for a bacterial assist.
“I said, ‘OK,’” said D’Agostino. “‘But let’s do a test first.’”
The bacteria passed the exam and did the job. On Monday, tourists admired the downward pensive glance of Michelangelo’s bearded Dusk, the rising of his groggy Dawn and Lorenzo’s tomb, now rid of the remnants of Alessandro.
“It’s very strange, especially in this time of COVID,” Marika Tapuska, a Slovakian visiting Florence with her family, said when she learned that bacteria had cleaned up the sarcophagus. “But if it works, why not?”
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