As with many of the best projects, things start by smashing stuff with a hammer. I use scavenged slate or other rocks that fracture into layers. I prefer to take my anger out on landscaping rocks looted from elven garden patios or poolside villas. Difficult part is achieving randomness with the cracks while also fitting the base and providing surface area for the miniature.
Next, I close up gaps with green stuff, cut green stuff spheres in half for bubbles (every time I have a bit leftover I just roll it into a ball), scatter some patches of sand & baking soda ash, and liberally apply Mod Podge to the lava surface to give it some variation (and smooth it out if it’s a GW base).
With airbrush: prime black, come back over lava with a few coats of white, and try to pick out some orange if possible.
Re-blackinate white overspray as needed and drybrush with grays. Wet blend using Warcolours fire set plus dark brown and white.
Usually a second pass at the wet blending where needed, add small areas of drybrushed orange/yellow glow to rock overhangs, scatter (without thinking too hard) brown/black floaty crustules. That’s pretty much it, thanks for reading!
Thanks for the tutorial. These come out looking awesome, and the use of actual stone makes for an authentic looking base. I used to source similar stone material from a hiking trail I frequented. Alas, I have now moved 2,000 miles away and no longer have access to that source; so I now substitute with sheet cork (not nearly as authentic). Well done!
Thanks for locating this appropriately @tjub, good call.