Useful Links on Toned Coins
Here are some Articles On Information for Toned Coins to perhaps help shed light on natural and artificial tone!
Toned Coin Articles
All About Monster Toned Morgans
Toning. Does it help, or hurt the value of a coin? - PCGS
The Tab Toning of Classic US Commemorative Coins
What Is Coin Toning and Its Effect on Value?
Collecting and Appreciating Naturally Toned Coins, Part 1
Collecting and Appreciating Naturally Toned Coins, Part 2
https://coinweek.com/collecting-appreciating-naturally-toned-coins-part-2/