The restoration work inside Notre Dame cathedral is ramping up.

Less than two years before the grand reopening, Notre Dame’s exceptional stained glass windows and paintings, which were spared by the flames that ravaged the monument back in April 2019, are now being given a fresh look.

This past spring, eight workshops of master glassmakers and artistic locksmiths were selected across France and entrusted with the cleaning and restoration of the cathedral’s stained glass windows.

“This is the first time they have been cleaned since … they were laid in the 19th century, 150 years ago,” president of the Manufacture Vincent-Petit and restorer Flavie Vincent-Petit revealed to ABC News.

“[Notre Dame] represents all the French and European medieval culture of the Middle Ages and how finally all these European nations were built around a spiritual impulse,” Vincent-Petit told ABC News, adding “It is extremely positive to be able to participate in the reconstruction.”

After months of preparatory work -- including decontamination against lead due to fire, documentation, and restoration tests -- the restorers are only now starting the delicate and arduous cleaning and restoration process.

But caring for Notre Dame’s stained glass windows is not solely a French affair as the Cologne Cathedral workshop from Germany has joined the effort by restoring the stained glass windows of four other high bays.

Another project in this huge undertaking is the restoration of 22 paintings out of the 25 removed from the cathedral post-fire.

Global donations for the project is an estimated at around €2,700,000 euros (approximately $2,703,000) and their restoration is carried out by 50 experts under the project management of the Regional Department of Cultural Affairs of Île-de-France (DRAC).

“No damage requiring the restoration of these paintings is linked to the fire of Notre Dame. These canvases are restored because they are old. Their restorations date back decades,” regional conservator of historical monuments at the DRAC Ile-de-France, Antoine-Marie Préaux, told ABC News.

At work since October 2021 in a secret location near Paris, the experts have been repairing 17th and 18th century works by masters such as French painters Charles Le Brun and Jacques Blanchard, as well as Italian painter Guido Reni, by sometimes recreating colors that no longer exist with the help of period documents.

Notre Dame is currently scheduled to reopen in 2024, five years to the day after the devastating fire destroyed the upper part of Notre-Dame Cathedral and the surrounding areas.