I was thinking of ways to archive simple data for a long, long, long time. So I thought of punched tape with data stored as 7 bit ASCII. Just go with me on this :-) Something like:-


The above is actually aluminized Mylar, but looks like what I'm asking about. For example, my PGP secret key is approx 7000 characters long. I would need $\approx$18m of tape for a standard 'paper' tape dot pitch of 0.1". Which I'd hope to store rolled up in a can.

Can this be achieved with stainless or titanium?

  • 1
    $\begingroup$ Why not chisel it into a piece of rock? less delicate machinery needed to retrieve it. $\endgroup$
    – Solar Mike
    Feb 16 at 14:15
  • $\begingroup$ Titanium , it would be much more expensive. $\endgroup$ Feb 16 at 15:39
  • $\begingroup$ @SolarMike Would it fit through a tape reader? $\endgroup$
    – Paul Uszak
    Feb 16 at 16:09
  • $\begingroup$ Would you class a tape reader as "delicate"? $\endgroup$
    – Solar Mike
    Feb 16 at 16:37
  • $\begingroup$ IMO, dot pitch of 0.1" is excessive. 0.031" would be plenty. $\endgroup$
    – DKNguyen
    Feb 16 at 21:01

2 Answers 2


As your question is specifically to determine if this can be achieved with stainless (steel) or titanium, the answer would be that it is not advised. Stainless steel is available in various alloys and is not listed in the ductility charts I've found. Titanium is listed and is less ductile than many other common metals. Chart below from linked page.

ductility chart

Copper, tin, and aluminum are likely to be much less expensive than titanium. Stainless steel is "typically" less flexible than other alloys of iron, but may be durable if the archived tape is not manipulated frequently.

My research shows that archival grade paper tape can survive decades of storage. The mylar tape in your image also qualifies in that respect. Mylar tape is common, durable, inexpensive and can be considered metal, as it is a metal film on a polyester substrate.

  • $\begingroup$ Titanium also has a no fatigue limit. $\endgroup$
    – DKNguyen
    Feb 16 at 20:59

The question isn't just the longevity of the media, but also the ability to read the media. There are people who have backed up on floppies, Zip disks and other formats that have no ability to read the media on modern computers. The odds that your tape reader will be connectable to a computer in the future is pretty low. Also, there is the question of how long you really need the archive to last. Archival paper can last hundreds of years if pigmented ink is used and it is stored appropriately (dry and in the dark).

I would suggest considering just printing your data on archival bond paper using a common 2D barcode format. Most ink jet printers use pigmented inks for black so that should be stable for many, many decades. You can use any available digital camera to read the barcode so that part of the process should be future proof. If you are worried about using a barcode, you could print to text and use OCR to read but this is less accurate than a barcode.

  • $\begingroup$ I would argue that you could use a digital camera to read punch paper too. And in a pinch, you could read a punch card by eye whereas it would be a lot more difficult with a barcode. Making devices to read punch cards is also easier if this is supposed to be civilziation surviving. $\endgroup$
    – DKNguyen
    Feb 18 at 18:31
  • $\begingroup$ @DKNguyen reading barcodes or text is already solved. The software is and will be available. Plain text printing will be easier to read manually too. Also it doesn’t seem likely that a punch device designed for paper is necessarily going to punch metal. $\endgroup$
    – Eric S
    Feb 18 at 19:58
  • $\begingroup$ Plain text printing would be more easily read by a human but not as easily read by "simple" technology which the OP seems to want by mention of a PGP key. I am not sure of the OP's context but I am approaching this from a doomsday time capsule perspective. $\endgroup$
    – DKNguyen
    Feb 18 at 20:01
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    $\begingroup$ As a "youngster" in high school, many years ago (last century), I amused myself by using the computer terminal connected to the University many miles away by dial-up and converting my homework Basic programs to paper tape. It was fun until authorities decided to remove that resource. Additional amusement was reading the dots/holes on the paper and matching them to my entered code. As @DKNguyen suggests, the MK 1 eyeball is capable. $\endgroup$
    – fred_dot_u
    Feb 19 at 0:40
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    $\begingroup$ Simple formats come with significantly higher odds that someone can make a new reader able to be connected to future computers. That is why you would use punched tape rather than say M-Disc CDs. $\endgroup$
    – user253751
    Feb 22 at 3:17

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