I made pure copper mirrors in 1970 as part of an infared lazer project. Copper is very soft, unlike speculum which is very hard, but copper grinds poorly, if at all. Being hard and brittle makes materials gring easier, soft means grinding is more diffcult. Actually the operative word is "friability". Friable materials grind easier. My perception is that speculum is a slow grinding material compared to glass. An appropriate tool is likely cast iron with the surfaces of both mirror and tool turned to the correct radius. Get ready for some "fun". In a few weeks you'll love glass