I also strongly reccomend the use as a finisher, Hastilite PO, marketed by Universal, as a nice clean alternative to rouge. Works very well with softer stuff like Pyrex and Bk-7, and produces a very low scatter, low RMS surface. We use it for SuperPolish, where after polishing, Hydrofluric Acid is used to etch the surface, which will reveal any subsurface damage, filled in by fusion during the regular polishing process.
Well, I guess that was 4 cents, sorry......
Bill Marriott Forest Knolls, Ca. USA btk@ix.netcom.com
P.S.--For real stock removal during rough grinding, I have played around with Boron Carbide, which is much harder than SiC. It lasts aprox 4-5 times longer, so it doesn't take much, which is good, as it is at least 4-5 times more expensive than SiC. And unless your real efficent in using it, it probably isn't worth using. (I use if for lapping Sapphire and Stainless Steel)