New paper only I presume? Grit extracted from used paper will be contaminated with metal, making it necessary to chemically clean re-cycled grit. Burning is another potential source of contamination.
Just a guess contamination might be an issue; I see lapping as a high-polish process, where the last thing I’d want to risk is scratches due to dirty grit.
Be interesting to compare laps done with new grit and those with Mick’s stuff. Needs a microscope.
Dave