Osagetree,
I do almost all my scrimshaw work with an X-ato knife....
1.) Prep the bone by getting ALL the scratches out of the surface using #0000 steel wool. The surface must be as perfectly smooth as possible, as the ink when applied will show up evey mark.
2.) Pencil draw on the bone what you want to scrimshaw.
3.) Trace the pencil with the X-acto knife, use a new blade, this will take a lot of pressure to scrimshaw the lines, be careful. Try and go over the whole thing once. Then go back and try and get good deep crisp lines.
4.) Take India Ink the good stuff, NOT water based ink. Spread it over the entire area you scrimshawed, let it dry for a few seconds, then steel wool the whole area lightly this will wipe off all the ink on the flat surfaces and leave the ink in the lines. You can go back and add details and repeat the process.... Give it a try, it's not that hard....
5.) Then For that aged look...I use Fiebings Leather Dye... Med. Brown... Just lightly apply... the more you use the darker it will be.... Get a good even coat... let it dry.... then buff it out for a nice shine....
Hope that helps.........