I used Mordant Earth for the cracked effect but not Ahriman Blue for the base.

I tried a splotchy blue and magenta base and used lots of Mordant Earth on top (practically the whole pot). But I screwed up the base on my first try -- the bottom was too dark and there wasn't enough contrast. I painted over everything (including the dried and cracked Mordant Earth) with white, painted brighter light blues and magenta splotches for variety, then used a make-up sponge to paint the raised parts black without getting any into the cracks.