You have an eye for detail Vimes. I spent quite a while to find out how effects like this can be achieved. One way is to select the Red channel in ps and smudge(finger painting on) to create a red displacement effect.
hehe cheers. I'll have to give it a go sometime. I love details like that in paintings though they add a great atmosphere, mood and style, stuff like that always draws me towards a painting :). Looking at your wip shot was helpful to, I like how all those rocks you made by simply but effectively using a few different brushes and values. I'd love to be able to paint more like that myself but I'm guessing you really need to know where to place values and colours to paint something in that style.
I am still trying to figure out value and tone. I just keep "fixing" stuff that seem wrong rather than knowing how it should be. What I am trying to say is, just dive in and experiment, take a break and return, flip and recheck. Sometimes improving the "debugging" methods one has can show some possibilities.