mineral oil, not the same thing as 100% mineral spirits (completely different). now if your going to put it on white, or natural bone, the mineral oil will darken it very slightly. If you use it on colored bone you wont notice much difference. However when you put it on colored bone, or any bone for that matter. do it lightly!! on colored bone, if you rub it hard it will take some of the color out, you'll notice it if you use a whit cloth. it wont be real noticeable on the handle unless you constantly do it (rubbing hard with cloth) many times. all you have to do is take a finger tip and lightly apply it (conservatively). It doesnt take much to protect!!! you can also use it on a stag, works really well. the idea is not to let the bone, or stag get to dry, causing cracks (over time). if you have a damper enviroment (not good for ther blades though!) chances are you will not need to do it, or often at all.