Artificially toned is some guy with a fry pan of oil and sulfur trying to rip people off on
ebay.
Naturally toned is a coin you put away and when you pull it out 20 years later it has some color to it.
Environmental damage is the unintentional exposure to some chemical or situation that causes some sort of surface color change such as a flood or hurricane (as mentioned on the forum before about a bunch of "colored" coins after hurricane "
Airbrushed toned is another scam used on
ebay to make coins appear naturally toned.
And now for the kicker: Intentionally toned. You collect coins and want to tone your coin. So you put it on a block of wood on the window sill or you wrap it in an non bleached napkin or in an empty mint velvet case or old Wayte Raymond album and "hope" that it tones. While not going all out to artificially tone the coin you are still guilty of trying to take a white coin and make it toned.
So where do you draw the line?

I am going with environmental damage on this one.
No one tried to AT it. And it didn't sit in a velvet box for 20 years to cause NT.
It just had the misfortune to be thrown in a mall water fountain with high chlorine levels or be dropped on the floor of someones car and after a few years of sitting on the carpet and being exposed to winter salt and high summer humidity levels this is what you get.