Maintaining a Bevel

Glass is much more prone to chipping at the edges for sharp angles (such as 90 degrees), so to protect the mirror I need to keep the edge beveled. When I was trying to get my tile tool worn down without changing the radius of curvature, the edges got ground more than usual and my bevel was almost completely ground away. To maintain the bevel, a sharpening stone (for knives) is drawn across the edge as the glass is slowly rotated. After one revolution the mirror and stone are both washed, and the whole thing is repeated. It took a little over an hour (or two Dr. Who episodes) to restore the bevel to an appropriate size.

Reached Target Depth

I finally reached my target depth! I moved the markers on my dial indicator. The one at 0 is still the target depth for an 8" f-5 mirror, but considering the bevel around my glass I'll really only have a 7.8" mirror surface. So the slightly shallower mark is for a 7.8" f-5, and I'll be satisfied if I end up somewhere between these two, closer to the shallow one.
My tool unfortunately is still not worn all the way through (the white patches are parts that have not been ground yet because the tile surface was slightly uneven). This presents a problem because these parts are not smooth yet, and may have a slightly different hardness than the worn-through parts. I switched to 120/220 grit because I ran out of 60/90, and I know I have more than enough of the 120/220. Using this finer grit it took a while, but I was able to finally wear the tile tool down until it was uniformly smooth.
In order to do this and not deepen my radius of curvature I had to alternate grinding with the tile on top and the glass on top, which ultimately removed glass from the edges and center equally. I overcompensated a bit, though, and ended up too shallow. I'll need to correct this before I move on to even finer grits.