Madura? dagger

[JamesKelly]

I'm new to this, have picked up a few points about flint & percussion American arms over the last three-score years, but am learning of my abysmal ignorance regarding knives. Well, perhaps the learning process will help stave off dementia just a little longer.

Was told by a helpful forum moderator that this was a spear, tombak, made into a dagger. Do similar daggers show up now & again out of Indonesia?

Whatever it is I like the bone carving & horn trim. Don't intend to inquire too deeply about whose bone was used to make it. Photo doesn't show the light and dark areas on the blade well, but it is a layer forged blade.

Is there perhaps a professional chemist on this site who could explain exactly how arsenic trioxide & lemon juice makes that crusty black color on a keris, or this spear/dagger, blade? I am a metallurgist with some knowledge of corrosion, steel and nickel alloys but know nothing about arsenic/AsO3 & how it might react.

I have the uneasy feeling that maybe I shouldn't handle that black stuff too much? Aside from harming the blade finish?