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Invisible Ink Printer Hack: Way Too Much Work For Something You Can’t See

by Paul Strauss

If you ever wanted to send secret messages using your computer, you could just embed secret messages in your image files. But if you want to print out hidden messages, you can hack your inkjet printer to print invisible messages.


The guys over at Make: put together this hack where you crack open the cartridge from your inkhet printer and replace they yellow ink with lemon juice. Print anything you want in yellow, and the page looks blank. But apply some iodine or heat the page with an iron, and your secret message will be revealed. Check out the overly complex and sloppy process in the video below:

YouTube Preview Image

It’s a huge pain in the ass, and looks really messy, but the results are kind of cool. Of course, you could do the same with just some lemon juice and a paintbrush or Q-Tip, but what fun would that be. This is way more geeky.

You can grab the full instructions from Make: here [PDF file].

Comments (1):

  1. Jimmy Bones says:

    I’ve been trying this approach with a Canon i860 I picked up at an estate sale and a hack of the yellow cartridge. I tried lemon oil, but this agent doesn’t seem strong enough to show via heat. I’ve also tried using blue invisible ink (OPTICZ blacklight reactive) with better success, but still not with the results I’d like. It would be a great technique to use on a map in a scavenger hunt, road ralley or geocache adventure if I could get it to work. My problem is that I’d like for the invisible writing to look something like the code written on the back of the Declaration of Independence in the National Treasure movie. Can’t exactly mimic that type of scrawl with a Q-tip! ;-)

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