I still think that baked clay tablets have the best bit retention rate of any media humans have invented. Doesn't take much skill to make or use them, either.
But for 500 years you're probably fine with acid-free paper, archival quality ink, and simple environmental control for storage (e.g., a well-designed box). Might want a nitrogen atmosphere, but it's probably not that critical.
But for 500 years you're probably fine with acid-free paper, archival quality ink, and simple environmental control for storage (e.g., a well-designed box). Might want a nitrogen atmosphere, but it's probably not that critical.