It’s the gold paint they used that acts as an air purifier when light shines through the glass.
[Associate professor at Queensland University of Technology] Zhu [Huai Yong] said that tiny gold particles found in medieval gold paint react with sunlight to destroy air-borne pollutants like volatile organic chemicals/compounds (VOCs), which are emitted from paints, lacquers, and glues, among other things.
“These VOCs create that ‘new’ smell as they are slowly released from walls and furniture, but they, along with methanol and carbon monoxide, are not good for your health, even in small amounts,” Zhu said.
When interacting with gold particles, sunlight creates an electromagnetic field that reacts with the oscillating electrons in the gold. This field resonates and breaks apart pollutants in the air, according to Zhu.
No wonder churches smell so great. I sense a new/old trend in Green building coming on. No more overpriced Sharper Image ionizer things; just glorious stained glass in every window.