Letterlocking

There was a cool article on this subject a few weeks ago: <a href="https:&#x2F;&#x2F;www.npr.org&#x2F;2021&#x2F;03&#x2F;02&#x2F;972607811&#x2F;reading-a-letter-thats-been-sealed-for-more-than-300-years-without-opening-it" rel="nofollow">https:&#x2F;&#x2F;www.npr.org&#x2F;2021&#x2F;03&#x2F;02&#x2F;972607811&#x2F;reading-a-letter-th...</a><p>Basically, opening centuries-old letters that are sealed with this technique is usually a destructive process: you might end up rendering some portions of the letter unreadable.<p>As such, many of these letters have never been opened! They might contain interesting things, but we have no idea.<p>Some researchers figured out a way to &quot;unfold&quot; X-rays of these intricately-locked letters, to render the letter legible without having to actually open it! It&#x27;s a pretty cool technique.<p>The underlying paper is here: <a href="https:&#x2F;&#x2F;www.nature.com&#x2F;articles&#x2F;s41467-021-21326-w" rel="nofollow">https:&#x2F;&#x2F;www.nature.com&#x2F;articles&#x2F;s41467-021-21326-w</a>

In the example image, it seems sealing wax is required to authenticate that the lock has not been opened.<p>If sealing wax is going to be used anyway, why not just fold the letter and seal with wax like normal?

Ah yes the original version of “warranty void if opened”.

There&#x27;s a sub-culture of origami related to this called &quot;Envelope and Letter Folding&quot;.

There was at one time a stapler-like device which did that automatically. It cut a slot and a tab, and pushed the tab through the slot.

Something like this is mentioned in the <i>Hagakure</i>, but I didn&#x27;t understand what it was for until now.