Credit where it's due. As far as I know, the idea of using C12 and C13 in diamond as bits to store information is due to Charles Stross. The earliest mention I've been able to find is in a July 2013 Usenet post from him. He later used the idea in his Hugo-award winning novella "Palimpsest," in which high-definition video recordings of literally all of history and prehistory in vast numbers of alternate timelines is recorded in a vast library which uses nearly all of Earth's carbon. (Coincidentally, I ran into him at a convention last weekend, the first time I'd seen him in years. Another coincidence is that "Palimpsest" is basically a rewrite of a novel written by the late uncle of one of the regular posters here.) Diamond is stable over at least billions of years, probably much longer. The rigid lattice means that adjacent atoms never swap. At normal temperatures and pressures it slowly turns into graphite, but that's so slow that it's never been observed at normal temperatures. So in practice, damage by cosmic rays is certainly the fastest failure mode, assuming reasonable storage conditions. (Do not store in a fire, or in molten iron, or smash it with a hammer. Pretty much anything else is okay, including storing it in water, acids, or solvents, or injecting it under your skin.) Its data density is an astonishing 10^22 bits per gram. In your shirt pocket you could store a full-lifetime video recording of every person who ever lived, with enough room left over for all books, newspapers, magazines, letters, web pages, emails, movies, and TV shows. The whole of Wikipedia and OEIS would fit into a microscopic speck of diamond dust. There's no evidence that substituting C13 for C12 in food causes any harm. There's some weak evidence that it, and other substitutions of a heavier stable isotope for a lighter one, may increase longevity. Deuterium is an exception. It's the only substitution that can kill. No non-microscopic organisms can survive total deuteration. Even so, there's weak evidence that drinking half a cup of heavy water per day might be good for you.