WIP of a reaper bones sarcophagus that I am trying a marble effect on for the first time..

Until OP replies I can tell you 2 ways I have done marbling in the past. the first try, which came out nice, was using a drier sheet I had used like 4 times to get most of the oils off it. Stretch it around really weird, then tightly wrap it on what you want to marble, then airbrush through it.

The easier way I also did it, and the effect I liked more, was when I used some medical gauze. Again, stretch it around, tear it a bit, make the square pattern go away basically, then, again, wrap it tightly around what you want to marble and airbrush through it.

It almost looks like gauze that OP used, but I'm not entirely sure.

You have to be careful with the drier sheet, beecause of all the oils in it. If you rub off a bunch of oil on your mini your paint won't adhere very well. At the same time you also have to be careful with gauze because of the regular square pattern it starts with. Both options have it's downfall, but I think if you take a drier sheet, use it a bunch of time, then actually put it through the wash you should be able to remove enough oils to not worry.

Hope this helps you a bit.

There's a video that explains the process using stretched baby wipes, I'll leave it here:

He was using cheese cloth as a mask, and I am assuming rattle can paint or airbrush white over a flat black. If you want to create more depth use a medium gray spray coat, then add more cheese cloth then a light gray spray coat then touch up with white for point of lights reflecting. You can also use a sponge if you are afraid of over saturating the white paint, or if you want to add a few flecks of a different color, usually blue or green. That last step is to varnish with a satin finish coat to give the polished look.

I made a quick tutorial for this a while back.