I've had pretty good results with the ARMEX Maintenance formula sodium bicarbonate blast media. I have to run it at the highest PSI my compressor can give (about 120 psi) in order for it to remove matrix relatively quickly. Still, that's only good with soft matrix. Anything hard, and it's almost worthless. I switch over to glass beads at about 30-50 psi, but you can definitely destroy a fossil with it. It's too abrasive. I'm wondering if anyone has used the ARMEX Maintenance XL, which is supposed to be 270 microns/70 grit, as opposed to the regular formula which is 170 microns/100 grit. Then again the glass beads are supposed to be 80 grit...