I got a lot feedback from the
40k Google+ community, so I thought I'd share it here.
Here is a closer look at how I did the lava bases for my marines
http://www.dakkadakka.com/dakkaforum/posts/list/634348.page#7566002 .
First I got some rocks from the garden, I put hot melt glue. I found hot melt was perfect because it looks like slow creeping lava. I sometimes put the rocks after I put the glue to get that sinking feeling. Make sure you try and let the glue distribute in a single direction. I did this by pointing the nozzle down directly for a small duration, then I moved in the direction I wanted. You can put heads, hands, or whatever inside the glue giving an even cooler effect.
I then spray painted black. The problem with the glue is that it's very smooth and so hard to get paint to stick. So I went over it with some dark red. I did that a lot of times until it worked with other paint paint layers. It was good too that the red hits sides of the rocks. After I got a full dark red coating, I worked from center. I put lighter red, then dark orange, lighter orange, yellow, then bright yellow. All separately, and each time I changed color I made a smaller line. And voila. You can swirl and do whatever you like.
Pictures here are flashed so you can see the intricate details, they look even better
irl