Billy if in doubt you can grade the grit yourself using water. The procedure is described briefly in one of A.G. Ingalls ATM books, you should own these; if not BUY A SET on ebay.
Personally I wouldn't trust the grit from a source that wasn't a reputable one with a firm connection to ATM - lapidary supplies definitely do NOT qualify.
The test will be when you think you've ground out the pits of a previous grade, inspect with a loupe. If you see scratches, the grit ain't what its supposed to be.
Cerium oxide is for polishing - not grinding - and is an alternative for black-rouge. In my mirror-grinding days I tried both. Cerium oxide polished faster but produced a rougher surface. On small surfaces (secondaries and lenses) it was so aggressive it isn't a good idea as the figure will be terrible and uncontrollable. IMHO not suitable for mirrors under 30cm.
Rouge is slower to polish, but produced a much smoother surface and better figure and ultimately a far better result - with patience and a lot of elbow grease. If you have the patience I would use rouge - not cerium oxide.
I continue to have doubts about your experience... anyone who has ground a few mirrors before would know these basic things.
Last edited by Wavytone; 02-07-2018 at 10:49 PM.
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