Ambient. I didn't elucidate my meaning well, what I mean by high levels of ambience, was those days when the majority of the light is ambient, (most days?!) so that even with judicious water spray and a bit of squinting, the carvings just don't show well. Bright days with good strong directional light work ok after a water spray, even when the sun's high up, provided you dance about a bit to find the right angle.

>use something like a matt black card to 'steal' some of the light on one side

I think this is the way to go. Possibly expanded to the point where you'd end up carying a makeshift bamboo frame, covered in blackout material, up to the tops of the moors.

An-n-n-ny waaaaaays....
Ms Mofflinson.
You ever gonna come visit Norfahmbahlahnd and make with the lovely painty-painty about the carvings? I'd love to see your take on Routing Linn or Kettley Crag.