You could include your nsec, npub and nsec.app password in your seedphrase backup. By stamping the words and number sequences on a flat metal base, the inscriptions become deep and visible, you can include a depth color and you can change the color of stainless steel (i.e. gold or carbon blue), with a simple gas stove or blow torch, WITHOUT damaging the inscriptions.
Discussion
26 washers - 12 for seedphrase and password, 12 for nsec, npub and nsec.app password, I managed to fit all sequences in 12 washers by using front and back of the washers. 2 washers are for privacy cover.
It's a work in progress and you will probably make many of these once you purchase the right tools.