Question about backup of Asymmetric keys

This - obviously - should be a last resort

not sure if this is the right place for this post

but I was wondering whats the best possible way to store a physical copy - if you had to - of your asymmetric keys.
One way that i found someone is doing is using QR code BUT a QR code for lets say ssh key is big , and bigger means its more error prone, so i am sure that there are some other way to represent text in an "encoded graph" that will be easy to scan and retrieve .

banks nowadays use phototan for secure transactions by encrypting codes into ...
photoTan

what are your suggestions people ?
@wendell

Qr can have a lot of error correction in it. Store 2 copies of nothing else.

punch cards?