I've made a couple using 800 grit silicon carbide. Worked very well, with no problematic "hot spots". The glass I used were old unexposed glass plates with the right dimensions for my Voigtländer Avus and Bergheil cameras. The glass plates also had the same thickness as the original glass, so they fit perfectly in their holders. I think Voigtländer originally used the same glass as plates was made of.
Originally Posted by AgX