A light scratch you could try using sandpaper, start with something coarse enough to get the scratch out, then use finer and finer. E.g 300, 600 then 1200 and finally buff it if necessry. I would find an old rubbish mouthpiece to practise on first.
Another thing would be to get hold of some black epoxy filler, e.g. Car body filler. Again practise first before trying I on your best mouthpiece.
If you can't get black filler, you should be able to get grey, and maybe add something like blackbird paint.
First you need to fix the ligature or switch to one that does not scratch. Locate the part of the lig that scratches the mouthpiece and bend it away from the mouthpiece or file/sand it smooth.
Deep scratches in HR can be filled with black Apoxie Fix-It. Shallow ones can be sanded out. But to get a shiny finish you need to finish with a polishing compound then a polish like Flitz. Usually not worth the cost and effort.
Yes as Mojo says, you'll need polishing compound if you want to make it shiny and new, along with a bit of elbow grease.
If it's shallow enough to sand out I usually do this: start with 320 or 400 grit to remove the big scratches, move to progressively finer sandpaper to remove the smaller scratches, go from 600 to 1200 to 200 after the heavier grit you started with. Then, take a soft cloth and some car-wax type gritty polishing compound and rub that on the area where you've been working. Afterwards, finally, take a chamois and some plastic polish (Kit car polish or Flitz, you need something non-abrasive for this), and go to town with the chamois. Rub the plastic/metal polish into the rubber and then use a dry part of the chamois to really rub the rubber to a like-new shine. This works for any hard rubber piece.
Of course, you'll want to stay far away from the playing surfaces like the rails and table unless you're deliberately trying to change something about the mouthpiece's playing surfaces.
A forum community dedicated to saxophone players and enthusiasts originally founded by Harri Rautiainen. Come join the discussion about collections, care, displays, models, styles, reviews, accessories, classifieds, and more!