We experimented with sugar & water, boiled up and left on greasproof to harden - this created glass-like shapes, however cutting it was difficult, and after a few days in the air the nice 'clear' look of the 'glass' went opaque.
Instead we decided to cut pieces of black icing and pipe-in the white frames.
I chose the Bridge Hotel specifically because it didn't look like it had many window to do.
When we visited the site we noticed all of the werrd and wonderful windows on the side facing the High Level Bridge. These in the pic above are all the different ones on this side.
Loved piping them - I felt like a pro :)