To state 50% of coins or whatever are AT is pure nonsense. Maybe 50% of the coins you or someone else buys are AT but the general statement is baseless. I collect world coins and many of my early 20th century coins on up are naturally toned. Most are inexpensive coins that no one bothered to clean and then retone, doctor to increase eye appeal or worth, etc. The countless world coins I own and encounter are more likely to be worn down or cleaned than AT, and far more likely to be in their natural state or toning than all else. Stating such a high percentage of AT coins sounds to me like either you are buying primarily US classic coins raw, like large cents or some other popular series. Perhaps this is what you had in mind, but even then the statistic you stated seems to high or just propaganda to try and sell more people on TPGs. This is just my opinion
I haven't read through all of this thread, but the last post about pre-1860 red copper brings up one interesting point. During the Bank Holiday of 1933 a number of large caches of red or near red copper from the 1850s were found and later dispersed. Any red copper from the 1850s with hard surfaces, and typically carbon spots, has a decent probability of having been from one of these discoveries.
Randall or Naftziger? P.S. Weren't coin doctors using cyanide compounds during this period? I don't doubt that full red copper from the early 1800s exists, but copper is so reactive and the doctors so good that I am very, very cautious.
Randall was found I believe within a decade or two after the Civil War. It is something I would have to look up again, but at one time I knew the history of it better. Yes, cyanide was often used during this time, too, but many of the practitioners "died out" so to speak. My point on the red copper is that it is absolutely unusual for pre-1860 copper to be naturally red, but those relatively few survivors can many times be traced back to serendipitous discoveries of bags of copper left in vaults and discovered in the 1930s.
I don't believe in 100 yrs old red copper coins just like some of you guys don't believe in 100 yrs old white silver coins. I am not a copper type coin buyer.