Tiffany glass is as expensive as it is because you can’t reproduce it. They destroyed the formula.
I’m sure much the same situation exists in the rose windows.
I just Googled “Images of Notre Dame stained glass windows,” but my computer is acting up and I could not paint the URL to transfer here. Look them up yourself. There are many different kinds of windows there. Some but by no means all have been destroyed. The glass parts are connected by double sided grooved strips of lead called “came.” Being of lead they are very susceptible to melting from heat. I also understand that the spire that fell had many tons of lead in it’s construction. Probably also melted and fell.
Regarding the formula. The church (Vatican) may have saved these formulas. Or perhaps the guilds kept them secret. My grandfather created his own glass colors for his work in the Indianapolis State Library. He also experimented with interesting effects. I have seen one glass he produced that was iridescent blue like a Morpho butterfly. Also another that was an iridescent satin surfaced rich gold. I’m sure that with the big money pledged for restoration, that this work can be done, though probably not in 5 years. I heard something like a billion dollars in pledges. Also money is now pouring in for the 3 southern churches that were recently burned.
“Tiffany glass is as expensive as it is because you can’t reproduce it. They destroyed the formula.”
Interesting, and a shame.
https://en.wikipedia.org/wiki/Tiffany_glass