On 2 Jul 2009 21:01:49 GMT, Adrian wrote:

Mmm. Mebbe get some samples, and see what's visible and what's not.

If you just stick a patch on it'll be visible even if 99.9%
transparent in visible light. However if you stick something neutral
to every bit of glass in every window, it will be "invisible"(*) as
all the window glass will look the same.

(*) Provided you don't go silly and stick a mirror film on. B-)

--
Cheers
Dave.