I may cross-post this in the stained glass forum, I'm not sure which is best. We have an older wooden 'feature window' and a friend made us a stained-glass insert to fit inside (there's a rebate there so the edges of the window
press up against it, and it's currently held in place with screws) - so the existing double glass is there, then a 3" gap or so, then the stained glass. There has been...