Find all your DIY electronics in the MakerShed. 3D Printing, Kits, Arduino, Raspberry Pi, Books & more!
vol16_92.jpg

HOW TO – Tuesday! Make an “Invisible ink printer” – Take A New Twist On Lemon Juice.
By Mike Golembewski

Lemon juice has been used as invisible ink for centuries. Messages written in lemon juice are invisible to the naked eye. However, when brushed with a mix of iodine and water, they become quite visible. You can use an updated version of this technique by modifying an
HP ink cartridge so that it prints in lemon juice instead of ink. Here’s how to do it.

TOOLS & MATERIALS
HP inkjet printer
Color ink cartridge
C-clamp
Hacksaw
Chisel
Latex gloves
X-Acto knife
Paper towels
True Lemon crystallized lemon juice ( 15 packets)
Small mixing cups ( 2)
Wide electrical tape
Zip-lock bag
2% iodine tincture

vol16_93.jpg

1. OPEN THE CARTRIDGE.

Clamp the HP ink cartridge to a workbench, with the leads facing down.
Use a hacksaw to cut a ¼” groove into the cartridge, at the gap between the purple lid and the black case.
Insert a chisel into the cut, and pry the lid open (Figure A).
Take off the lid.

2. CLEAN OUT THE YELLOW INK.

The ink will stain skin, so wear gloves. Use an X-Acto knife to remove the yellow ink sponge from the cartridge (Figure B).
Wash the sponge in a sink until the water runs clear (Figure C).
Squeeze out the sponge, and put it aside.

Take a paper towel, and use it to clean the ink from the sponge holder in the cartridge.
Repeat this, getting all the way to the bottom, until the towel comes out clean.

3. MAKE THE INVISIBLE INK.

Fresh-squeezed lemon juice is not strong enough to work as invisible ink in a printer, so you’ll need to make a concentrated mixture.
Do this by using True Lemon crystallized lemon powder.
Add 4tsp of water to a mixing cup, and then pour in 15 True Lemon packets.
Stir until the powder is dissolved.
Soak the sponge in this mixture for 10 minutes.
Make sure it’s completely saturated.
Push the sponge back into the cartridge (Figure D).
Replace the cartridge lid and seal it shut with electrical tape.

4. PRINT THE INVISIBLE INK DOCUMENTS.

Put the modified cartridge in your printer.
Create a solid yellow image at letter size, 8½x 11 (Figure E).
Keep printing this until no yellow ink appears on the prints.
Once the pages look empty, the printer is printing only in lemon juice, and you’re ready to go!

To make a secret message, print documents with solid yellow text and images (Figure F).
The yellow areas will print in lemon juice, and will be invisible to the naked eye.


TIP: Once you’re done using your invisible ink cartridge,
wrap it in plastic and put it in a zip-lock bag; otherwise,
it will dry out.

5. EXPOSE THE INVISIBLE INK!

To reveal your secret message, make a mixture of 1 part iodine tincture to 10 parts water.
Brush it over the page.
The message will remain white, while the rest of the page will turn pale blue!

Photography by Mike Golembewski

Michael Golembewski is an artist and interaction designer who lives in Boston. For more of his work, go to http://mwgstudio.com.

References:
http://mwgstudio.com

make16sma.jpg

From MAKE 16 – Page 92. To get MAKE, subscribe or purchase single volumes.

Phillip Torrone

Editor at large – Make magazine. Creative director – Adafruit Industries, contributing editor – Popular Science. Previously: Founded – Hack-a-Day, how-to editor – Engadget, Director of product development – Fallon Worldwide, Technology Director – Braincraft.


Related

Comments

  1. Dick Vonski says:

    No picture of the end result? The ‘decoded’ message, i mean.

  2. Phillip Torrone says:

    it’s there, on the first page… it’s invisible.

  3. The Oracle says:

    Hey, my printer turns into one of these every time it runs out of ink.

    Actually, this does sound kind of interesting. I’m just curious how they get it to put out enough juice. I did it with a paint brush as a kid and I had to drench the paper. And how fine a working resolution can they get, again as a kid my letters were over an inch tall I would also like to see a picture of the end result to see the results they can get.

  4. femke says:

    i’ve looked at a few videos and they all use yellow. is there a specific reason,or is yellow just the easiest to use?

  5. jay says:

    can you suggest any alternative juice brand, True Lemon is not available here in the Philippines, pls pls pls.

    Thanks in advance

    Jay

  6. jay says:

    Can i used 4C Totally Light 2 Go Lemonade instead of True Lemon? Please suggest if ever you’ve try something else, True Lemon is not available here in the Philippines..

    I hope to receive a reply from you guys ASAP, Thanks,

    Jay

  7. jacob redwolf says:

    will vinegar work 

  8. jacob redwolf says:

    will vinegar work 

  9. jacob redwolf says:

    will vinegar work 

  10. jacob redwolf says:

    will vinegar work 

  11. jacob redwolf says:

    will vinegar work

  12. jacob redwolf says:

    will vinegar work

  13. jacob redwolf says:

    will vinegar work

  14. csjamesadams says:

    Hmm! Sounds pretty awesome. I think it’d be a great way to create really detailed maps of scavenger hunts and other games for kids.

  15. Danny Strain says:

    To bring the invisible ink so you can read it you can also use a candle. Place a lighted candle below the sheet and heat the paper but don’t burn it. the letter will be readable.
    Regards

  16. Barts a plopping says:

    I would strongly suggest using a hot 40-watt lightbulb for cooking the invisible ink to brownish visibility.

In the Maker Shed