Is there a risk of the ink fading over time or the coin becoming generally unusable due to decay? That's my biggest concern when considering buying or selling a coin. Is there any information out there that speaks to the general expected longevity of a casascius coin? What if we hold out on selling a coin only to learn that the BTC on it is no longer accessible which torpedoes the actual total value?
I’m just guessing but I’d be pretty sure that some sort of scanning electron microscope will always be able to read the private key even if it’s not visible to the naked eye.