Metal seed backup

A metal backup is the same 12 or 24 words copied into something that outlasts an emergency. Common 304 stainless steel melts above 1,400 degrees Celsius and titanium above 1,660, while aluminum gives up at 660, which is why the alloy a product is made from matters more than what is printed on the box. Get the material right once and this is a problem you never revisit.

How it works

Fewer characters go onto the plate than people expect. The BIP-39 English list of 2,048 words is built so that the first four letters identify each one uniquely, so "aban" is as good as "abandon", and a 24-word backup is 96 characters rather than roughly two hundred. Number the positions as you go, because sequence is part of the secret and an unnumbered plate found face down is a puzzle.

Three marking methods, with three different life expectancies.

Stamping with a hardened punch set displaces metal instead of removing it, which is why the letters stay readable after fire has scaled the surface. It wants a hammer, a steady hand, and one practice run on a scrap piece.

Centre punching a dot pattern reaches the same depth more slowly, with fewer ruined plates.

Letter tiles dropped into a slotted housing assemble fastest and disappoint most often. Heat and pressure can free the tiles, and words shuffled into the wrong order are as useless as words that burned. Surface treatments sit shallow for the same reason: laser marks, acid etch, paint and plating can all be lost to scale or corrosion, and the coating is usually the first thing to fail.

Material choice is short. Solid 304 stainless handles fire. Grade 316, which adds molybdenum, holds up better against salt and chlorides and is worth the small premium near the coast. Titanium takes more heat than either and costs accordingly. Aluminum belongs nowhere near this job. Jameson Lopp's repeated stress tests, which torch, crush and dissolve commercial products, keep reaching the same verdict: assembled and coated designs fail where a solid stamped plate does not.

Where you see it

Buy a plain stamped plate and check the listing states the alloy and the thickness. Assemble it at home, offline, from words your signing device generated in front of you, never from a card that arrived already filled in. Do not photograph the finished plate, since a phone photograph is a cloud photograph within seconds, and never send it to a commercial engraving shop, which amounts to emailing your wallet to a stranger.

Then think about where it lives, which is the part metal does not solve. A fire-rated document safe is engineered to keep paper below its ignition point, a job your plate does not need. What the plate needs is somewhere a burglar will not search and a demolition crew will not sweep away, in a different building from the signing device, and recorded in a note your family can find.

Keep any passphrase off the plate. Stamping an extra word under the twenty-four collapses a two-factor setup back into one factor, and whoever finds the plate then holds everything.

Finally, restore from the plate alone. Wipe a spare device, type the words exactly as the metal reads, and check the resulting first address against the wallet you already have. A backup nobody has ever restored is a hypothesis.

Metal seed backup vs hardware wallet

A metal plate is the backup; a hardware wallet is the tool that uses it. Conflating them produces a matched pair of mistakes. The first is keeping only the device, on the assumption that the coins live inside it, which ends badly when it is lost, dropped, or wiped by a PIN nobody in the household remembers. The second is leaving the plate in the drawer beside the device, so one burglary or one fire takes both. The device can be replaced by any vendor in an afternoon. The words cannot.