Jseitz 12000 is already a pretty high level of finish. Mothers on a rag will also help get them shiny. I prefer not too high of a gloss on horn, otherwise they just look like plastic and you start to loose some of the depth. I have done very little work with plastic but have found mother to clean up older scales quite nicely. If you do want to get a super high gloss finish on the horn you can use the polishing cakes on a buffer and run through the same progression you would use for a high polished steel. Just be careful not to be too aggressive or you can get the horn hot enough to warp.