Originally Posted by
ubeaut
Not trying to be smart here but....
Abrasives, glass, tungsten, scrapers, etc won't help, only good woodturning technique and sharp tools used correctly will clean up those nasty rings by not making them there in the first place.
Ebony isn't an easy timber to turn unless you have good turning skills. Those groves could be sanded out in a soft timber but not in ebony. However with good turning technique they wouldn't be there in softwood or ebony, so shouldn't need to be sanded out.
I'm sure others will agree and may give you some tips. The best tip I can give you to fix the problem is to get some lessons from a skilled turner. Maybe have a look on line and see if you can pick up some insight into turning goblets with clean smooth cuts.
Doesn't help with what you have right now unless you can re chuck and turn the inside again but might be of help for future goblets and other hollow objects.
Cheers - Neil :U