I've eaten more than that, but doing this isn't a great idea unless you have a very large tolerance, and are very well versed in deep psychedelic trips. Taking that much at once makes it hit you within minutes. It kind of feels like getting kicked in the head by a horse or something. It's almost painful and kind of feels like your brain is going to pop. Then if you can stay conscious, it pretty rapidly brings every aspect of your personality right to the front of your mind.
It feels what I imagine schizophrenia feels like, and then there is a climax, often accompanied by a visionary experience. It's not like trails and distortions, like you get from lower doses, but for me anyway, I saw complete ideas and visions, as if I was being pumped full of information. There are flashes of different objects or concepts playing out inside my head while I am unaware of my surroundings. I could go into detail about specific trips and visions, but generally they all show me how I am one with all the energy of the universe, and I see multiple points of view about anything I think of, all at once. I have experienced this, then opened my eyes, and every person was just a pastel, transparent glowing orb or aura.
And yes, I know people who have eaten raw crystal, including myself. I haven't ever seen anyone take a whole thumb and stick it in a jar, then lick it off. More often than not, people take a finger, get enough that you can see some visible crystal, and then lick it. Still many people consider this being "printed", but I guess it really isn't if you want to be technical. The amount that would fit on a full thumbprint I imagine could be 500+ hits, even. I know a couple people who have done pretty close to what some may consider a full thumbprint, but at that point, they need a baby sitter for sure, and it lasts for a few days.
A friend of mine took a thumbprint, and couldn't talk for a day or two, and he crapped his pants, as well as other unpleasant things. He had to have a girl sit and take care of him the whole time. But by about day 3, he could form sentences and was starting to come back around. He is fine now, and a very good buddy.
So yes, "thumbprints" are real, but the majority of people who talk about them, probably aren't actually doing a full thumbprint, but more like a 1/5 of a pinky tip print or something.. Also, for the stories about how you have to take a thumbprint or something before you can purchase it, that isn't very common nowadays, but I don't know for sure about the 60-70s. I know there are people who make others eat some raw when they're trying to make a large purchase, but this is probably a much more individual thing, and not really some common standard among all circles involved with it.. I could go on more about that, but I don't want to go into anything about dealers or anything.