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.
the cartridge (Figure D). Replace the cartridge lid
and seal it shut with electrical tape.
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.
4. PRINT THE INVISIBLE
Put the modified cartridge in your printer. Create a
solid yellow image at letter size, 8½× 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.
Photography by Mike Golembewski
3. MAKE THE INVISIBLE INK.
Fresh-squeezed lemon juice is not strong enough
5. EXPOSE THE INVISIBLE INK!
to work as invisible ink in a printer, so you’ll need to To reveal your secret message, make a mixture of
make a concentrated mixture. Do this by using True 1 part iodine tincture to 10 parts water. Brush it over
Lemon crystallized lemon powder. Add 4tsp of water the page. The message will remain white, while the
to a mixing cup, and then pour in 15 True Lemon rest of the page will turn pale blue!
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
Michael Golembewski is an artist and interaction designer who
lives in Boston. For more of his work, go to