I wasn’t expecting this,
but the volunteers at the class expect me to continue working on my mirror at home! So after the class, I went on a shopping trip for a few essentials (a bucket, a plastic tray, sponges, spray bottle, that sort of thing). Monday evening I wrapped some 120 grit sandpaper around a block and put a 1mm bevel on both mirror and tool. Took about half an hour. Perhaps using a stone would have been quicker, but Johan suggested the sandpaper method as giving better control, and because you can get sandpaper finer than your grit at most grades (this is important, apparently, to avoid pits on the bevel’s edge being a point of weakness).
Last night, after putting the girls to bed, I spread newspapers liberally all over the coffee table to grind away while my wife watched television. It turns out that it’s impossible to hear the TV over the noise of #80 grit scraping away between the two pieces of glass. Who knew! Still, after about 90 minutes I’d managed to get visibly closer to full contact between the mirror and tool. The picture left shows the tool after Saturday’s class, and the large hollow off-centre which hasn’t yet been touched by abrasive is clearly visible. That hollow is now reduced by about a third. I haven’t yet measured the sagitta, so don’t really know how much progress I’ve made since Saturday. I’ll do this before I start work again this evening.