Originally Posted by
Euclid440
And… just so you know… glass is not flat.
Try lapping a piece, with a diamond plate, flat-ish, but not flat.
A Chinese stone will eat a Diamond plate. Loose Silicone Carbide grit and a steel cookie sheet, is fast and efficient, about $15 buck will do several stone. Search lapping Ark stones.
The cookie sheet and Wet & Dry, on a flat concrete floor works well for finishing grits. Once flat it goes quickly. Hope you used a respirator with your belt sander.
The EBay Chinese stones run the gamut on grits, but none I have seen are close to 12 or 15k.