Eight glass manufacturers from France have begun the painstaking operation to clean and restore 39 high windows in the medieval cathedral's nave, choir, transept and sacristy.

The Notre-Dame suffered extensive damage in a major fire on 15 April 2019, fortunately most of the historic cathedral's stained glass was able to withstand the heat and the flames. However; the windows were heavily soiled with smoke and dust, blocking external light and obscuring the range of colours of the 170 years-old glass. The glass-cleaning process involves gently rubbing the surface with cotton soaked in water and ethanol, a delicate and repetitive process aimed at collecting deposits without damaging the window. According to Flavie Serriere Vincent-Petit, head of the eponymous stained-glass company in Troyes, southwest of Paris, who has been given the task of restoring 22 windows, the windows is now in a major cleaning phase, to wash off both the blaze's dust and the dirt resulting from human breath, as well as candle soot. The cathedral has been closed for restoration since the April 2019 fire gutted its roof and sent its spire crashing through the vaults below. France is aiming to reopen the cathedral, which dates back to the 12th century, by 2024 when it hosts the Olympic Games. Notre-Dame's stained-glass windows were created by architect Eugene Viollet-le-Duc, who also designed the 96-metre (315-feet) spire. Master glassmaker Marechal de Metz created the cathedral sacristy's stained glass. "Master glassmakers of every age engaged in creating a sacred space through light...Our task today is to reproduce that colourful vibration that Marechal de Metz and Viollet-le-Duc wanted to recreate in the 19th century," Vincent-Petit said. The workshop of Cologne Cathedral in Germany is also helping with the reconstruction by restoring the stained glasses of four high windows.

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