The burnisher end is used on floss or thread bodies, the brush end is for dubbing. These have no finish on them, just polished with Brasso which has a small amount of wax in it. If the wood seems a bit dull I will apply a tiny bit of hard wax and rub it almost dry. There is no finish to wear off and the little bit of work done by the burnisher to the floss is not enough to stain the floss. I just did a bunch of Alaska Mary Ann variations and all have white or cream floss bodies and none showed the slightest trace of discoloring.
I have used metals, obsidion, antler, horn, ivory, teeth, baleen, and woods... The shape is the issue far more than the materials. Be veycareful with antler though because the outside can be very thin and the porous center will snag floss terribly. Caribou antler is especially thin on the outside. Some kinds of horn will fray and tear up your work, too.