How To Store Bitcoin in Stainless Steel (Cold Storage)

This guide will show you how to store your Bitcoin (ether, dash, or other cryptocurrency) in durable stainless steel dog tags ($9) with a fairly inexpensive metal stamp kit ($20). Video at bottom.

If you have more crypto than you'd normally carry around as cash in your wallet, it's recommended to store that in cold storage which means offline, or at an address with a private key that never touched the internet. An easy way to do this is on a paper wallet, but paper can be destroyed by fire or water.

Stainless steel won't corrode in water, and melts at over 1300 deg C, which is well beyond the 800 deg C typical house fires reach (according to the internet).

Supplies

metal stamp kit ($20) - 4mm tall letters recommended. This kit has numbers and capital letters only. This is great for recording 12-24 word recovery phrases, hex (0-9, A-F), and even keys with lowercase letters. I just make a dot under the letters to indicate lowercase.
stainless steel dog tags ($9)
hammer - 1.5 lb or heavier recommended
stamping block - or anything hard you can hammer on - be sure to grind afterwords so your private key isn't visible!
prick punch - a small nail will work, too.
masking tape & ruler - to help line up letters
safety glasses & ear plugs - metal on metal can create sparks

Generating an Offline Address

Go to bitaddress.org and save the web page to a USB key.
Copy that to a computer that's not connected to the internet.
Open the page and follow the instructions to generate an address (just move your mouse around for a while).
We're going to stamp the "Private Key WIF Compressed" phrase. The video explains the difference between all these numbers in more detail, but the main advantage is that this one has error checking built in. If you mess up one number, bitaddress will tell you this when you double check it. This format also leaves out confusing letters like upper case "I" and lowercase "L".

Note: I also use this technique to back up my hardware wallet, which gives me a 12-24 word phrase. The neat thing about word phrases is that you only need to write down the first 4 letters of each word, and the dog tag can easily fit 4 rows of 12 letters. More details at BIP39.

Note 2: You can even generate an address by flipping a coin 256 times, but you still need some software to convert that into an address to send money to.

Stamp the Private Key

There are 52 letters / numbers, so that comes out to 13 letters on 4 rows.
Use the tape to provide an edge you can line up the stamp to for each row.
I've got about 40mm across, so I space each letter 3mm apart and mark this on the tape.

I also mark every group of 4 and each row on my piece of paper to help keep track of where I am.

Slide the stamp down until you feel the bottom edge of the letter hit the tape, and give it a good whack.

If the letter doesn't come out clear enough, you can usually hit it again. If you stamp the wrong letter entirely and don't want to start over, just use the punch or nail to cross it off.
For lower case letters, use a nail or punch to put a dot under the letter. I found this easier (and cheaper) than getting a stamp kit with lower case letters and trying to tell the difference between upper and lowercase.

Test Reading Back Your Key

Type your stamped key back into the offline computer that has the bitaddress site on it under the "Wallet Details" button. Make sure it doesn't give you any errors and that the resulting Bitcoin address matches the original one. You might even want to wait a few days to make sure you're not just typing from memory.

Send Bitcoin to Your New Cold Storage Address!

You now have a secure and durable offline cold storage wallet, send some money!

Cleanup

Grind or file down whatever you were stamping your tags on to make sure you don't leave an extra copy of your keys around.
For maximum security, format the hard drive of the computer you used to generate the key and throw it into the ocean. :)

Video Version

Inspiration

I was originally inspired by a product called CryptoSteel, which comes with prestamped metal letters, but costs $80 and up. One advantage of Cryptosteel is that it has a lid, so someone that randomly comes across it doesn't see your private key without opening it. You might want to tape over your dog tags or put them in a container to provide similar protection.