[stevejb]

You can print QR code with different heights representing white or black. That piece of plastic would last a long time, and you could encode.....something. You could pint a version 40 (177x177) grid with a Prusa XL easily, and that would last for a few thousand years and be waterproof and fairly resilient to a lot of things. You could probably print a 177x177 grid on a regular Prusa MK4 and just have a color change layer. E.g. layer 1 white, and then layer 2 black. This would be 2,953 bytes.

You could even get a binder, and then print the QR codes sheets as 'pages'. You could print these thin enough to do 1mm sheets. That means ~ 120 of these in a 5 inch binder. So, a 3 ring binder of 1mm sheets of 177x177 QR codes would hold about 346.2 KiB. You could store encryption keys in this way. You can probably push the density well past 177x177 even on a Mk4s pretty safely. I may try this later today.

[RobGR]

I don't think that piece of plastic would last as long as you think. I think even ABS or PETG would be crumbling to powder in 100 years.

But you could use it as a stamp for thin sheet metal, that might last a longer time.

[stevejb]

Yeah it seems like a cheap CNC drill which can drill holes in steel sheets would be something that would last basically forever. Something like this:

TTC3018 CNC Router Machine 3-Axis Engraving Machine Metal Engraver GRBL Control with Built-in WiFi, 775 Spindle Motor, Engraver Desktop CNC for Wood, Acrylic, Plastic, Aluminum, PCB Milling & Carving https://www.amazon.com/TTC3018-Machine-Engraving-Engraver-Al...

[stevejb]

Hey I just did a bit of a deep dive into this. Wow, thanks for pointing this out. It seems like 'PEEK' would last the longest, but most printers can't do this.

"Standard estimates for indoor PETG longevity are 10–20+ years under normal conditions, with some sources giving a more conservative 5–10 years. A century is 5–10x beyond those estimates under passive conditions." Wow! Thanks for pointing this out. This is fascinating.

[RobGR]

Or, press it into soft clay and then fire the clay.