[Intralexical]

I've experimented with this using one of the commercial print-on-demand services. Not filament, a binder-jet sintering marine stainless steel type of process, IIRC. Slightly modified Noto Sans Extracondensed font with... Let me check the files... 0.1mm line width, 0.45mm lower-case "m" width, dense letter and line spacing, gets 3KB ASCII per square inch. ...Engrave, don't emboss, or the letters will come off with impact and corrosion!

Filling the engraved letters with black wax makes it optically legible under a good handheld magnifying glass. Then rub with vaseline/mineral oil/wax/ACF-50, mount on a brass holder (check relative galvanic corrosion order!), store pressed against aluminium or zinc sheet sacrificial anodes Just In Case(TM), inside polyamide or ABS case. Should last basically forever.

I designed it for manual reading, so the holder doubles as the "reader". Basically just a spindle going through a hole in the disk, holding a margin in the edge and center of the disk. The text is a spiral, so you can spin the disk to help keep the viewed region aligned under a higher-power microscope.

For home printing, probably the way to go is Formlabs wax resin (or equivalent), then either learn brass casting yourself or hire a jeweller to do it. Though you won't get as good resolution/density as the metal process I tried. And really, laser engraving'll probably be cheaper and better. Consider if good-quality paper and ink, maybe laminated, inside a Pelican case'll be more practical.

I wouldn't personally trust any of the common plastic printing materials to hold up for important data under oxygen, UV, fatigue, heat cycles. Are you sure the resin's not overcured or undercured, the filament fused correctly and won't delaminate, it won't reach the glass transition temperature during summer? And bacteria is already evolving to eat plastics. Maybe SLS/MJF polyamide's okay, but in that case, I'm not sure I'd trust the sintered structure for small details (and they don't have great resolution anyway).

> The assumption was that using common 3D printer measurement tools (like for bed-leveling) would provide a way to read back whatever data was encoded onto the surface.

> And then, obviously, if that proof of concept exists, I'd wonder about some kind of advanced version that used specialized equipment for the reading (and possibly the writing/printing).

At these small amounts of data, specialized read hardware just adds risk IMO. Plain text can be read manually or with OCR. QR codes can automate reading with a standard flatbed scanner or smartphone camera.

Consider ideas for encoding: Plain text, B64, hex, Reed-Solomon codes... 1-bit depth structure turns most of 3D printing's storage density into redundancy, but anything truly 3D adds read risk. If you insist on automating reading, QR codes will get you error correction, encode/decode software, and COTS hardware for "free". Personally I think human readability is a big advantage too. Maybe OCR text, and put error codes in a QR beside the text for byte-perfect computer input?

Compare: Memory of Mankind uses ceramic tablets in a desert cave. Arch Mission Foundation project uses holographic glass. Long Now Rosetta Disk engraves with electron beam on nickel, IIRC was/is also commercially available for personallized jewellery. M-Disc and Bluray (HTL?) have modern digital storage density, good stability, work with commodity hardware. ...See design considerations of prior art for digital storage in 2D, naïve 3D version is to just use these as a heightmap:

- https://github.com/cyphar/paperback - https://github.com/za3k/qr-backup/ - https://github.com/colindean/optar - https://github.com/Sjlver/psst - https://github.com/schroeding/paperstorage - https://github.com/intra2net/paperbackup

Also, don't sleep on the centuries of work done by archivists and historians! The top comment is right; acid-free archival paper has very good overall cost, density, stability.

[catapart]

You make great points! I appreciate the detail of the comment, and I don't particularly disagree with any of it. I think someone else mentioned gravestones that are etched and filled with black, so your suggestion of just doing that with sensible scales and fonts seems like a slam dunk, to me.

Bummer that it doesn't really seem feasible for a hobbyist, though. I take your meaning with the wax and such, but I think my solution would just be to go bigger and store less data. And I mean bigger like, 20 characters per print bed, or something. But then, at that scale, maybe a QR code would hold up well enough in plastic, too?

Overall, I think I've mostly learned that "archiving format" is a broad term that really needs to be collapsed by describing how the archive will be stored (and what extremes/complications to expect). In any case, thanks for the links and again for the detailed discussion!

[Intralexical]

> I take your meaning with the wax and such, but I think my solution would just be to go bigger and store less data. And I mean bigger like, 20 characters per print bed, or something. But then, at that scale, maybe a QR code would hold up well enough in plastic, too?

Only way to know is to try it! I think you might be surprised. QR codes (with high redundancy settings) are very resistant to corruption.

The idea with the wax is to transfer the data into a more durable final product... Lost wax casting, you print wax, cover the wax in plaster, melt the wax, pour a metal (or epoxy) into the plaster mold.