IF you want to scrimshaw a buffalo horn, polish it first, then do the work.
I have seen multiple colors of enamel or acrylic paints used on these horns- red, blue, gold, white, green, yellow, etc.-- to highlight the scrimshaw work. The paints fill in the cuts( scratches?) in the surface, and then a light rub of the surface with a fine abrasive after the paints dry removes the excess paint from surrounding surfaces.
Do the darkest colors first, dry them, and then remove those excesses, before applying the lighter colors. This will avoid the problem of dark paints mixing in with the light ones. Some carvers( scrimshawers?) will cover the finished parts with the dark colors dried, with tape- like the blue painters tape-- to protect the paint while they work on the next color.
Once finished and all the paints are dried, cover the entire horn with a clear varnish, or acrylic finish to seal in the paint and give the horn a final gloss finish. You can buy spray cans of acrylic finish that do an excellent job. There are also "Clear Coat" products sold for use by automotive repair shops that can be used to protect horns. I believe the automotive product is a lacquer, not an acrylic varnish.
Using paints- particularly colors different than just white- really make fine scrimshaw work "Pop" on these horns. I saw a horn with an American Eagle scrimshawed on it ala the National Seal, done in red, white and blue, that really attracted everyone to the artist's table.
I would not personally choose to carry such a fine horn in the woods on a "Trek" or hunt, however. That would be an "Art" horn, displayed but never actually used.