PARIS, FRANCE - JANUARY 29: Notre Dame Cathedral is seen during restoration work more than nine months after the fire that ravaged the emblematic monument on January 29, 2020 in Paris, France. A fire broke out in Notre- Dame Cathedral in the evening of Monday April 15, 2019 and quickly spread to the building's wooden roof destroying the famous spire. The building cleaning and consolidation phase should continue for a few more months. (Photo by Chesnot / Getty Images)

On April 15th, 2019, a fire started in the attic of Notre Dame, an 850-year-old cathedral housing priceless art in the form of paintings, stained glass, and an organ boasting 8,000 pipes.

In this fascinating piece at Science Magazine, Christa Lesté-Lasserre describes the multi-disciplinary effort to decontaminate the structure and its artifacts from lead released during the fire and to evaluate every limestone block to determine whether, after the porous stone releases water absorbed during the blaze, it can be re-used to restore the structure.

Amid the destruction, scientists have discovered opportunities to learn where the limestone blocks were quarried, as well as how 13th century stonecutters chose each stone’s placement and the order in which portions of the church were built.

The charred remnants of attic timbers have stories of their own to tell, says Alexa Dufraisse, a CNRS researcher heading the wood group. Variations in thickness, density, and chemical composition of growth rings reveal climatic conditions year by year. “Wood registers absolutely everything while it’s growing,” she says. Notre Dame’s oak beams grew in the 12th and 13th centuries, a warm period known as the Medieval Climate Optimum. By connecting the growth ring record with what’s known about economic conditions at the time, researchers hope to see how climate variations affected medieval society, she says. The shape of the beams also intrigues the wood team. Long and narrow, they clearly grew in a dense, competitive environment, Dufraisse says. That supports the “silviculture” hypothesis, the idea that the trees were purposefully reserved or farmed for the cathedral. Their age at cutting—about 100 years old—would suggest people were planning Notre Dame several generations before construction began. The location of that forest is another mystery Dufraisse’s team is tackling, using the beams’ chemical composition. The Paris area is likely, but boats might have shipped wood along the Seine from farther away. Soils contain levels of strontium and neodymium isotopes that vary from region to region, but stay constant over the centuries—especially at the depths tapped by the roots of oak trees. So her group is seeking to match the wood’s isotopic makeup to that of soil in likely locations. “These questions will also be pertinent if we’re looking at meeting the requirement of reconstruction that’s identical to the original,” she says. As for Maurin, he’s investigating the builders’ marks on the roof support beams. Applied by men shaping the beams on the ground, they were meant as instructions for the assembly team working more than 30 meters above them. “It was kind of the IKEA of the Middle Ages,” he says.

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