Copper slag or coal slag? This stuff looks very dirty. I have a customer who wants me to install a synthetic turf into her back yard because it's too shady for real turf to grow well there. It will function as part of a kid's playground. But I am concerned that if I install your product using the infill you recommend that her kids are going to end up with black "coal slag" residue all over their hands, knees, arms, etc. Is this stuff dirty at all? Or will kids be able to play on it and stay clean?