acid free archival paper. archival ink. Even non archival books can last quite awhile I personally own a book that is over 120 years old. Don’t sleep on books.

2kb is about 4 double spaced pages. Why not just write it out and store copies in multiple locations?

There’s some kind of glass based storage which will last centuries, but it’s kind of bad against scratching, so that’s something to worry about. I believe Microsoft was building a data center with it somewhere.

1 to 2 Kb isn’t all that much. Write it down on acid free paper. Use plain ink with a good binder, neutral pH, UV resistance is generally optional in this case, but better. Better safe than sorry. Store it away from light in low humidity at temps <16 deg C. Seal hermetically. Use oxygen absorbers.

If cameras are still around why not just write out the text on a metal tape, like aluminum foil, with holes where ink would be if printed. That way, the encoding (QR or whatever) is not the issue.

You might be looking at the wrong thing. The problem isn’t likely to be the medium over that time period, it’s much more likely to be the perception of the value and use of the thing.

I have 100+ year old records, furniture, art, electronics, documents etc. a few were built to last but most are normal consumer grade stuff from times before.

They are still kicking around not because of their uniquely good quality or archival construction but because someone before me thought to keep ahold of them.

So you probably have three new problems to solve: how to get your message on something that people won’t just throw out, how to get it on as much stuff as possible to minimize the changes it’ll be thrown out and what format will actually be recognized as an indicator of something worth investigating as opposed to just another dead link to a Chinese user manual.

What kind of data is it? If it can be printed, you can just print it and store it somewhere safe, or print multiple copies and distribute it around. Plenty of 80 year old books are perfectly readable. That’d only be books printed in 1946 so nothing crazy. You can pay for professional printing so they can do it on good quality paper and so on.

Plate of stainless (the non rusting kind) and laser cut a QR like code through it like a stencil. If they can’t get a good read on the plate with a camera, you can lay the plate down on paper and spray or dab stencil paint through the holes to form a flat image on paper of your QR

I actually think there’s two facets at play here. There’s the first dimension, the durability of the medium itself against the environment, which is what you’re asking about. The second dimension is redundancy. It’s all well and good if you invest in aluminum but something heavy gets dropped on your plate and the singular copy is damaged beyond recovery. Worth considering that if this information is important enough to etch in metal, you should make several copies across a few different storage mediums in a handful of physical locations. A safe deposit box may not be a bad idea, for example.

Find a good cave and etch it into stone.

Cryptosteel if kept in a fireproof container should easily last past 200 years.

I thought about this a little bit, and there’s an interesting possibility here. If you make a mold, you may be able to cast a QR code in concrete. If poured well and stored in a place that isn’t completely hostile, it should last as long as you need it.

I recall seeing a video a few years ago about a storage medium that does precisely this, stored data in the position of the metal ion of a perovskite. Although I can’t find the video anymore.