I like the survivability, and the constraint to be doable with common hand tools.
For more information density, and easier readability by a less-technical person who inherits it -- at the cost of requiring special tools -- I wonder about using number&letter stamps with a hammer.
Or, if you permit very special tools, laser-cut alphanumerics (base16, base58, or base64, for arbitrary bits; or alphabetic passphrases). Either engraved, or cut fully through, like an old drafting lettering stencil.
This is a problem the cryptocurrency community has been dealing with for almost a decade: how to securely store a seed phrase backup (48 characters, the first 4 characters of 12 words).
Letter stamps are one option. A number/letter grid you use a simple punch with are much more dense than this but still easy to do with hand tools. There are lots of products with pre-made stamped letter tiles that slide into slots.
For more information density, and easier readability by a less-technical person who inherits it -- at the cost of requiring special tools -- I wonder about using number&letter stamps with a hammer.
Or, if you permit very special tools, laser-cut alphanumerics (base16, base58, or base64, for arbitrary bits; or alphabetic passphrases). Either engraved, or cut fully through, like an old drafting lettering stencil.