Some accidental R&D - completely CG ink bleeds using Particular. Yeah, yeah, I know we have all seen shit loads of ink bleeds and it's old news... But the cool thing about this technique is you can create any shape you want, control the speed of the bleed and dispersion, and the edge detail is based on fractals so it's scaleable (unlike raster image maps or masks). And check out the subtle way the dark, dense spots "dissolve" and disperse... Happy accidents :)
I think the real power of this would come out in texture mapping - next step is to pre-render some patterns and use them as texture maps in C4D.