"Smokey" ) writes:
In the 1960s I ruined many a crystal following the guidelines found in ham
publications then for raising the frequency of my FT-243s. Of course I used
Comet or Ajax since that was all that was available.

I'm with Pete, I don't think the abrasive matters while how you do it
does.

If you grind too much, that will kill them. And as Pete says, if what
grinding you do is not nice and even over the surface, that will cause
problems.

If you don't clean things properly after the actual grinding, that may
stop oscillation.

Michael VE2BVW