You’d probably want to put it somewhere it isn’t going to get moved a lot. There are concrete additives you can mix in to help with the strength of the finished material as well.

Here’s a link to a genuinely fascinating dive into concrete: https://m.youtube.com/playlist?list=PLTZM4MrZKfW90PdaBFt70BLTbz1bTF6Mn

I also figured that if you made your QR code so that the black sections were slightly raised, making it a working QR code could be as easy as dipping it in white paint, letting it dry, then painting the tops of the raised sections black.

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 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.