We are in the zone between chemistry and art. Definitions differ between venues. Mostly I think you are correct.
Diversion...true story...while in graduate school, one of my friends who lived in a trailer woke up and was trying to decide what day it was. Chemistry graduate school, you live, eat, sleep and breathe chemistry, so this guy didn't have a TV, a radio, no newspaper, and cell phones were still in the future. He called the operator to ask what day it was.
This is all very simple. Corrosion is bad stuff that eats away the surface of the metal. Verdigris is bad stuff on copper that is green. Patina is good stuff (that could be green or not). Toning is good stuff that could be just about any color, unless it's black and on a coin minted after around 1600 (then it's environmental damage), or it's blatantly artificially induced. There. Subthread over, lol.
When I called PCGS to ask them what a double die was I told this guy I had this coin that I got from Ebay that I spent my entire paycheck on and I found out that I had been cleaned. He told me to take egg yolks I think it was or whites I forget which said you put them in a bowl of water let them sit by the window seal for a while and then to take a battery and hook a wire to the positive and 1 to the negative and the tape one of them to the coin and then to stick the other one down in the egg and water and wiggle it around and it would make it toned like natural looking. Is that true or is he pulling my chain?
Besides the toning, it's probably not the best idea to spend one's entire paycheck on a problematic coin. If you can return it, do it. And as @Paddyman will emphatically tell you. it's doubled die, NOT "double" die.
Acrylic fingernail polish. Jewelers use "liver of Sulphur" ( Amazon) on heated silver objects. Even the most skillful say to do matching items such as ear rings at same time as outcome is "Unpredictable". Read the precautions using chemicals that are unfamiliar . Jim
Serafino, he was describing a homebrew electrolysis system. The egg yolks contain sulfur , and the polarity of the wires are very important !! jim
I strongly suspect that day has been here for several years, just only the "in" people know or don't care , as long as it passes. I think most is already in the current market prices. IMO , Jim