The black sand I found had a glossy texture, which is perfect for lump coal. I just smeared flat black craft acrylic paint on the carved foam and sprinkled the black sand on it. Worked like a charm. I should also mention I also picked up a bag of white sand from the same store to experiment with. It is far too light for limestone in this region, I'm thinking I could color it with gray of some sort and come up with a closer color to limestone.... perhaps a budget alternative to ballast. I don't think I'll have time to work on that in the next couple weeks, so that is something to keep on the back burner for now.