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I used to work in a integrated circuit debugging lab. We had a pulse laser that we would use to ablate the layer of glass on top of the metallization so we cou

by aiscott 15y ago

I used to work in a integrated circuit debugging lab. We had a pulse laser that we would use to ablate the layer of glass on top of the metallization so we could probe the die. While goofing around I discovered that I could vaporize the ink of dollar bills. The largest area per pulse was pretty small, 25 microns if I remember right. Maybe 100. So it wasn't very practical, but it worked. I don't remember if I tried it with pen ink. It might work okay for ball-point as that mostly lays ink on top of the paper. You'd still have the impression in the paper from the pen though. Ink that didn't soak in but lay on top of the paper would probably stand a good chance of working. Maybe gel ink?

DanBC 15y ago
There used to be a scam in England where people would use solvents to wash away the postmark from posted letters, allowing them to sell / re-use the stamps. I can imagine a group stealing a laser to remove the postmark. Luckily, UK stamps now have other security features. (http://www.telegraph.co.uk/news/uknews/5400999/Royal-Mail-launches-tamper-proof-stamp.html http://www.telegraph.co.uk/news/uknews/5400999/Royal-Mail-la...)
cs702 15y ago
Thank you. That's what I thought: any dark ink that just lays on top of (i.e., isn't absorbed by) the paper could probably be vaporized in similar fashion by a pulse laser. Anyway, when I wrote that, I had an inkling that someone in HN would know probably something about the subject matter, but I never expected anyone to have real-world experience using pulse lasers to vaporize ink from a piece of paper, let alone dollar bills! Awesome. This is why I love HN.