Fenestra: Stained Glass Guide

Light has been a building material for nine hundred years. Fenestra gathers the long story of coloured glass — from the cobalt lancets of Saint-Denis, where an abbot argued that jewelled light lifts the mind toward heaven, to the opalescent lamps and landscape windows that Louis Comfort Tiffany fired in Corona, Queens. Every entry is a window with a history: who cut it, what the glass was made of, why certain blues were never matched again. The app opens in a dim nave of deep plum, and the panels glow out of it one by one.

The heart of Fenestra is The Light Hour: tilt your phone and a low sun swings behind the window on screen, the leaded panels brightening and dimming as the angle changes, exactly the way a real window is never the same twice in one day. Beyond it lie a Chronicle of eras from Romanesque to Art Nouveau, a Glossary of the craft's own vocabulary — came, grozing, grisaille, flashed glass — a Panel Book where you write your own notes on windows you have stood under, a shelf of Kept panels, and a Glazier's Test that asks whether you can tell silver stain from pot metal. Nothing needs a signal; the whole cathedral fits offline.