How do you back up a seed phrase on metal?

A metal seed phrase backup is a copy of your wallet's recovery words stamped, punched or assembled in metal so it can outlast a fire, a flood or decades in a drawer. The words themselves are the same 12 or 24 words a wallet shows at setup. Why that phrase controls everything is explained in what is a seed phrase. This guide covers how people move it onto metal and what can go wrong.

Why back up a seed phrase on metal?

Paper is the usual first backup, but it is fragile. Coldcard, a hardware wallet maker, notes that paper ignites at about 233°C while house fires often reach 600 to 1,000°C. Brief contact with water can make writing unreadable, and ink fades over the years.

Grade 304 stainless steel, the common material for metal backups, melts at roughly 1,400 to 1,450°C and resists rust in fresh water. Coldcard puts the typical cost of a metal backup at about $30 to $150, against nothing for paper.

How do you put a seed phrase on a steel plate?

There are three main methods:

• Stamping. You hammer letter punches into a blank plate. Bitcoin developer Jameson Lopp, who has stress-tested many metal backups, rates this as the hardest method to do well, citing missed strikes, rotated letters and worn jigs.
• Punching or engraving. You mark dots on a pre-printed grid with a center punch, or scribe letters with a rotary tool. Lopp suggests center punching as easier to get right.
• Tiles. Pre-made letter or word tiles slot into a holder, with no tools needed.

You do not have to record whole words. The BIP39 list has 2,048 words, and each one can be identified by its first four letters, so "abandon" can be stored as "aban". Coldcard says this roughly halves the characters to record.

What makes metal seed phrase storage fail?

Lopp's tests point to several weak spots:

• Aluminum can melt into slag in a fire, so stainless steel or titanium is preferred.
• Loose tiles can scatter if the holder breaks, and putting 24 words back in order by trial is practically impossible. Tiles that carry the word's number help.
• Thin plates, screws and nuts can bend, fuse or seize under heat and crushing.

Where the backup is kept matters as much as what it is made of, as what happens if you lose your seed phrase explains.

What should you check after making a metal backup?

Check every word against the wallet screen, letter by letter. Coldcard advises running a full recovery test before you move significant funds, because a mis-stamped character fails just like a faded one. Exodus recommends keeping copies in separate secure places. If you use a passphrase, keep it apart from the words, as described in what is a seed phrase passphrase. Trezor says its metal backup also works with its multi-share backups, where each share can go on its own plate, as covered in what is a Shamir backup.