This grinding/polishing disc is around 40kg (88 pounds). I have to clean it extremely well every time I switch from one grit stage to the next, as any previous grit left on the disc can cause scratches — one of the most feared moments because it means you have to start over and spend several days polishing again to get rid of that scratch.
Polishing optical glass to achieve optical transparency involves several stages. I use an automatic machine that runs with silicon carbide and cerium oxide. Although the process is slower, I find it safer than using a polishing machine with diamond pads.