At LRMH, the laboratory tasked with conserving all the nation’s monuments, [LRMH Director Aline] Magnien and her 22 colleagues apply techniques from geology to metallurgy as they evaluate the condition of Notre Dame’s stone, mortar, glass, paint, and metal. They aim to prevent further damage to the cathedral and to guide engineers in the national effort to restore it. President Emmanuel Macron has vowed to reopen Notre Dame by 2024, and he has appointed a military general to lead the operation, which involves many government agencies and has drawn philanthropic pledges of about €1 billion. But it is the LRMH scientists who lead the critical work of deciding how to salvage materials and stitch the cathedral back together. And even as they try to reclaim what was lost, they and others are also taking advantage of a rare scientific opportunity. The cathedral, laid bare to inspection by the fire, is yielding clues to the mysteries of its medieval past. “We’ve got 40 years of research coming out of this event,” says LRMH Assistant Director Thierry Zimmer. . . . The porous stones call for a different approach. One possibility is plastering them with a latex “silly putty” that can be pulled off along with the lead dust, [geologist and head of LRMH’s stone division Véronique] Vergès-Belmin says. A similar method uses a clay-based compress that dries and contracts, creating lead-filled “chips” that can be collected and disposed of. A third idea is to use laser cleaning. The scientists will begin to test various methods in two of Notre Dame’s chapels later this month. “We’re most likely looking at a combination of techniques,” she says.