Wooden sheaths ,or saya, should be made from wood types that are dry, soft, and non acid. That is why Ho Wood is typically used. The outside can then be stained or painted as wished. Using ornate woods with pretty grain and patterns is tempting, but the nature of those woods will lead to scratching and or corrosion of a blade left in the saya. If it is just for show, and the blade will rarely or never be in it, OK....but is that what a sheath is supposed to be.
The other way to deal with this is to make a liner for the sheath. It is made from a wood that is suitable, such as Ho ,Bass, or Balsa. Two strips of such wood are inlaid in channels cut in the two slabs of showy wood. After that, the softer wood is carved out to form the blade channel. Once the two sides are glued together, the soft core protects the blade and the showy outside wows the observer.
BTW, blades should not be stored for long times in wooden sheaths if possible. Regular oiling is also a maintenance requirement to protect the blade.
Similar to the above lining technique, you can cut the blade channel oversized and line it with leather or felt. Use only acid free materials ( vegetable tanned leather). This works well on a tanto size saya.
