On Sat, 17 Oct 2009 07:50:46 +0100, Ian White wrote:

something to alter the infrared signature of parts of the stone
wall.
Any ideas?

Whole-wall IR LED display, programmable with your MOTD.

That appeals but not to the wallet. B-)

Don't really need to emit IR(*) though just alter the heat signature
of parts of the wall. Would black paint under the white do that?

(*) I don't want to dazzle the night vision camera as they fly up the
valley towards us at 500mph...

--
Cheers
Dave.