"Cleaning Notre Dame With Light"

This is going to be a long process.

From WBUR - Boston Public Radio, December 21, 2020:

Cleaning Notre Dame 'With Light': Expert Says Lasers Will Help Restore Cathedral To Former Glory

The rebuilding of the 857-year-old Notre Dame Cathedral in Paris is entering a new phase.

The cathedral's massive organ has been disassembled ahead of schedule for cleaning. And workers have removed construction scaffolding that melted during the catastrophic fire last year.

With the cathedral’s roof now gone, scaffolding is being constructed inside the building, says Time magazine Paris correspondent Vivienne Walt.

Restoring Notre Dame has led to new discoveries about the cathedral, such as that it’s not perfectly symmetrical, she says. And workers have reached the cathedral’s vaults for the first time in hundreds of years.

“No one had actually seen the top of this cathedral close up until now,” she says. “The fire, ironically, as tragic as it was, has become an absolute lesson for a whole range of different artisans and scholars.”

The lead roof melted in the fire, and dust coated the entire area. The schools and other buildings in the surrounding area — one of the oldest parts of Paris — were decontaminated after the fire.

Researchers believe there’s a large amount of lead contamination inside the building, she says. When Walt went inside Notre Dame after the fire, she had to wear a hazmat suit and shower upon leaving.

“Every single thing that touches the cathedral cannot be taken back out on the street,” she says. “So they're very, very serious about the lead pollution.”

Walt says she visited the “cavernous, dark” but crowded cathedral many times before the fire. Now, one of the most monumental places of worship in the world — that once saw 14 million tourists a year — is “echoing and empty.”

Architects point out the building looks worse than it is, she says, though the fire did ruin the 300-foot spire, the roof and a large part of the medieval oak vault covering the ceiling....

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The other use of lasers is, of course, the almost miraculous good fortune that Professor Andrew Tallon was able to complete his mapping of Notre Dame a few years before his death in November 2018, five months, almost to the day before the April 15, 2019 fire.

Here's one of our posts from that week:
Easter 2019 
Dr Andrew Tallon and the rebuilding of the Cathédrale Notre-Dame de Paris 

By now you've probably heard about Professor Tallon and his laser, the billions of measurements and the images created from the data:

ExtremeTech, June 2015

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If interested see also:
What's Holding Up the Work On La Cathédrale Notre-Dame de Paris?