Quoted:
Depends on the material used.

Canvas, linen, etc probably won't take that kind of luster because the cloth layers are so porous but paper isn't too hard to do.  Sand like you normally would and take it to 400 at a minimum.  600 or 800 would be better.  From there, I cheat and use a buffer wheel on my bench grinder with some white or green polishing paste.

Then, I wipe it down with a rag soaked in Brake Parts Cleaner to strip off the paste wax.  When the material is dry and dull looking, paint it with cyanoacrylate (Krazy Glue) and let it dry.  This seals the material.  Buff again and it's done.

All of these were made from the same batch of micarta--old bed sheet, a little OD Ritz dye and fiberglass resin.

This one was sanded/buffed/sealed as described above.  You can see on the curved parts where the fibers didn't take a polish as well as the flat spots.

<a href="http://s1162.photobucket.com/user/fighterfixer1/media/springfield014.jpg.html" target="_blank">http://i1162.photobucket.com/albums/q527/fighterfixer1/springfield014.jpg</a>

This one was just sanded and buffed.  Again, the curved contours didn't take nearly as much shine as the flats.

<a href="http://s1162.photobucket.com/user/fighterfixer1/media/LeafSpring1.jpg.html" target="_blank">http://i1162.photobucket.com/albums/q527/fighterfixer1/LeafSpring1.jpg</a>

This one I left it rough for a better grip

<a href="http://s1162.photobucket.com/user/fighterfixer1/media/BAK2.jpg.html" target="_blank">http://i1162.photobucket.com/albums/q527/fighterfixer1/BAK2.jpg</a>