again a tin lap with 50,000 diamond powder—no oils of any kind as it just slides your stone over polishing agent. use a (very) slow speed to polish and a drip rate about 20-40 seconds– make the diamond powder, applied by finger tip,a muddy slur. the diamond will charge into the surface a little to prolong polishing. i have students and past students using this way/method and have polished smoky over 150+ carats with very little problem. i have a quartz egg over 400 carats polished this way and right now a laser YAG over 2000 carats that will be an egg, polished that way on same lap.