[semi-extrinsic]

A friend of mine had an incident with these pens in high school. Used one on his physics midterm exam, teacher put a laptop blowing hot air onto the pile of papers before grading, so 3/4 of every page were just gone. He had to retake it.

[TheKnack]

If you put the paper in the freezer, the ink will reappear.

The ink doesn't really go anywhere, even when you use the "eraser". It just becomes transparent. This can be reversed by exposing it to cold.

Pilot mentions this on their tips and tricks page: https://www.pilot-frixion.uk/uk/tips-and-tricks/

[colordrops]

But if you erased a lot then the page would be a mess after everything re-appears.

[analog31]

Wow, that's just like the secret spy pen from the Johnson Smith catalog. Brings back memories.

[dqv]

That’s too bad. He could have just put it in the freezer to get the ink back. Uh, but let’s keep that between us.

[CamperBob2]

Spoiler: that was the physics test. He failed.