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Posted by Robert May on November 6, 2002 21:16:41 UTC

I think that the 301 size is the next size although I really haven't dealt with that system.
I will also note that when you get to the smaller sizes, pits even from the 90 grit could still be present if you didn't get rid of them when going to the other smaller grits.
For the 301/303 question, try a wet with the 303 grit and see if the grinding action is louder and, if so, that is the next grit you should use.
If you were using the right sized grit, you may want to go back to the previous grit and get rid of the pits you have found and then proceed back to the finer grits. Depending upon the way you grind and how long, you will probably need about 10 wets to get rid of the pits from the previous size of grit at a minimum. Also note that the finer grits last longer than the coarser ones do and the limiting factor often ends up being the amount of ground off glass that you end up in with in the grit.
I usually stop at the 320 grit size and take a look at the glass with a 5x loupe and find a few pits that are exceptionally deep looking and mark where they are on the backside and grind until those are gone before going to a finer grit. With the fine grits, I then use a distant (10' -20' away) reflected light bulb, getting the glancing reflection of the bulb to an orange color and then move the glass so that I can see if the color is the same across the mirror - the deeper the color, the coarser the grind is.
Good luck!

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