But today, “restoration is the cutting edge of art history,” said Emilie Gordenker, director of the Royal Picture Gallery Mauritshuis in The Hague, whose museum is also planning a major exhibition centering on an in-depth restoration of a single painting, “Saul and David,” which she described as riveting as a “crime scene investigation.” Using the latest technology, the museum will chronicle the discoveries of its creation and history — every unexpected detail that lurks beneath the canvas, initially considered to be one of Rembrandt’s finest but later de-attributed. “We live in a time when the public wants to look behind the scenes and museums are finally becoming more open about it,” Ms. Gordenker said.

Italy’s Uffizi Gallery in Florence, for example, had conservators working in a glassed-in lab so visitors could watch the action. Right now, in Belgium, Jan and Hubert van Eyck’s “Adoration of the Mystic Lamb,” better known as the Ghent Altarpiece of 1432 — one of the world’s most famous panel paintings — is undergoing a seven-year restoration. Financing from the Getty Foundation in Los Angeles has helped pay for it, including an interactive website showing the work in minute detail. (The public can also visit the three sites in Ghent where it is being restored.)

“This is a shift and I think a very important one,” Luke Syson, the Met’s curator in charge of European sculpture and decorative arts, said of this new tell-all era. With Adam, he added, “there’s no pretending that the breaks aren’t there or that this didn’t happen. Yes, this awful accident occurred on our watch and now we are also responsible for its resurrection. Our processes need to be transparent.”

In decades past, museums would have also restored a damaged work of art in a way that got it back on view as quickly as possible. In the case of a massive marble sculpture like Adam, conservators would have resorted to using iron or steel pins that required drilling many of the sculpture’s joints. But such invasive work can be risky, curators said, potentially harming the marble.

Then there was the option, popular in the case of ancient sculptures, of leaving masterworks unrestored if they cracked with age, excavation or accidents — a process conservators often call “the romance of the fragment.” That was the case with the Louvre’s headless “Winged Victory of Samothrace” or its armless Aphrodite of Milos, better known as the Venus de Milo. “There was a trend in conservation to take away all restorations from ancient sculpture and get down to the original fragment,” said Ms. Riccardelli, the Met conservator who led the work on Adam. “But now we see the value of a Renaissance restoration.”