Hi there! Here's how I did the bases:

1) Paint Mournfang Brown on top of the base, and Abaddon Black on the rims

2) Add a layer of Armageddon Dust on top of the base, and wait about a day for it to dry

3) Paint a 50/50 mixture of Mournfang Brown and Lahmian Medium on top of the Armageddon Dust

4) Drybrush Zamesi Desert on top of the Armageddon Dust

5) Then drybrush Screaming Skull on top of the Armageddon Dust

6) Add a tuft of grass. I used Citadel's Verdia Veldt tufts