With the black with gold web, even razor sharp tools (and even sanding) will cause a blowout because of the heat build up. I make tons of Georgia Bulldog Pens (red gemstone with gold web and Black gemstone with gold web) The red is never a problem. I have found that the answer to turning the black is to dip the tool (VERY SHARP carbide skew workss best for me) in water after about every 3rd or 4th pass. Even if it cuts ok, sanding may blow out the black if it gets too hot in the process.
After a little time with the black, I can tell when it is time to wet the tool just by how hot my "guide thumb" gets on the skew.