That's a pretty terrible picture, you know.
I know my camera sucks huge black cock. I can't do any better.
What kind of wood is the box made out of?
It's actually plastic. Clear plastic with brown plastic corners. It's a neat little thing... I'm pretty sure when I bought it it came with some little chocolate gold doubloons.
...THE FUCK WHY?
Because olive oil works very well at removing grime and dirt from the surfaces of coins. So does pure acetone and WD-40, the latter of which I've tried before (I need to try acetone, from what I hear it works best on silver coins though).
You can also use muriatic acid (pool chlorine) to temporarily see the date on a dateless Buffalo nickel (one that has had the date worn entirely off). It's pretty cool, tried that a year or so ago.