You can also get grit from hobby shops or specialty shops selling rock polishing supplies. For rough grinding the grit doesn't really matter that much so you could go this route without trouble, but for fine grinding I would suggest using grit from companies that supply it specifically for mirror grinding.

: Try Willmann-Bell or Newport Glass or even Edmund Scientific. : Anybody that is selling mirror kits usually will sell the grits : or even the grit kits seperate. Unless you are making a very short : FL mirror don't bother with the 80 grit for your 4". That stuff works : very fast. At Stellafane this year, I took an 8" blank with a convex : surface and in the space of 3 hours of work and talk, had a 36"fl. while I was : getting others to push the glass for a minute just to get the rough : feel of how to push glass. : Have Fun and Keep Looking Up! Bob May