I have glass of varying widths (all 3/8 thick)I use the 3 X 11 most.They are acid etched with hydraflouric acid to provide a frosted surface to hold the various grit pastes I use .They are made from float glass,and are flat to within a couple of light bands.This is the same stuff we used to sharpen surgical instruments in the old days before they became disposable.It costs less than a dollar to make a 3 X 11,and they last a long time,maybe 50 razors before the frosting get worn down,and they lose their flatness.You can make some really sharp,smooth edges.You can use diamond paste.I use oil soluble pastes(I dont use diamond too much),and give it a shot of WD 40 every once in awhile to keep the medium in suspension.Best Regards Gary