Question.
Which kinds of grit should I use to polish away the scratches from the surface of a section of plastic-embedded undecalcified bone? Any other advice would also be appreciated.
Answer.
Try using a series of fine grit grinding papers before going to the polishing cloth with 1 æm alumina slurry. Remove scratches progressively, by going to a 320 or 400 grit, then 600 grit. Grind with a figure 8 motion, and rinse well between grits. Then go to your 1 æm alumina polish, figure 8 motion, and use Buehler microcloth (velvet type surface) that comes in sticky back, can stick to a plastic surface, or whatever to prevent slippage, polishing takes only a few (2 or 3) minutes. Examine under a magnifying glass for scratches. The first grits for grinding depend on the grit size of your diamond cutoff blade. There is a way to read the codes for this grit: if you have a 320 grit size of diamond, then go to 400 grit (Norton waterproof paper, Tufback Durite) paper first.
Be sure to flow water across tilted grinding surface, to wash bone "dust" and plastic away. I like grinding paper taped to a thick plexiglass rectangle, with one end slightly elevated with a rubber handled hammer. It's cheap! The 1 æm slurry (small amount) should be put on a slightly wet polishing cloth; that way it will polish more easily and quickly. For a mirror-smooth surface, go to 0.1 æm alumina slurry after the 1 æm.
I have tried progressive alumina slurries, 3 æm then to 1 æm, but it was a waste of time, 1 æm worked just as well. Polishing away scratches after 600 grit paper worked well. Finer grits (800, 1000, 1200) didn't help that much and were expensive.
Equivalents are:
400 grit = 22 æm
600 grit = 14 æm
800 grit = 10 æm
1000 grit = 5 æm
Whatever you do, protect your joints from the stress of grinding and polishing. Use holders. The ergonomics of polishing will eventually take its toll, damaging your finger joints - want a photo? Buy an automatic grinder and polisher if at all possible. This was the best investment we ever made, but too late!
Gayle Callis
(uvsgc[AT]msu.oscs.montana.edu)