Table Top Gaming - Terrain - Craters #1

When I dug out those resin Generator pieces, I stumbled upon some old Pegasus Hobbies Craters. So I thought I would give one a whirl and paint it up whilst the airbrush was out. Here is the progress, thus far, with just primer, base layers and a few blends to bring the grey crater to life. What do you think I should do for the outside of the crater?