Carbon steel, so you don't want to store it in the leather sheath. ESPECIALLY if that sheath has gotten really wet. Oil it lightly with an oil you wouldn't mind getting in your food if you are likely to touch food with it. If it going to be stored for any length of time, I wrap it in length of cotton cloth.

The sheath is good leather. I use neatsfoot oil on it as needed- doesn't need it often. If it gets wet, I set it in a warm place with air convection as soon as I can.

The leather washers are the only place I do anything odd. *blushing* I use the skin oil from alongside my nose. I know it sounds really gross, but it is symbolic/symbiotic in a way. It is also the best performer that I've found, neatsfoot allowed it to dry too quickly.

Despite the care, I prefer the leather handle becuase it doesn't get stupid at very low temps like all but a handful of synthetics will, and works just as well at high temps. The steel butt on some of my Ka-bars aren't so pretty because they've been used, but it works well for things like tent stakes.