Picture of 25-Cent Invisible Ink/Pen (UV light visible)
Have you ever wanted to get one of those cool invisible ink pens from the store so you can write secret messages to your friends? Or maybe you need to use it to mark peoples hands for admission to a party. With this Instructable, you can easily do so, and do it for only 25¢!!

Step 1: Gather The Materials

Picture of Gather The Materials

There are very few materials needed for this Intstructable. These are listed below:

1 Highlighter (I got a pack of 4 different colors for only $1)
1 cup (plastic works best, so you don't have to worry about washing it out)
3 Tablespoons hot water
cotton swab

Step 2: Take Apart the Highlighter

Picture of Take Apart the Highlighter
-If you want to make the pen, be sure not to lose or break any parts.
Start by taking the cap off. set aside.
Using the pliers, grab and pull of the front plastic piece of the marker.
Next, slide the ink cartridge out of the back of the marker.
Then, also using the pliers, pull the tip of the marker out.

Step 3: Extract the Ink

Picture of Extract the Ink

This step is not hard at all.
Place the foam ink cartridge and marker tip in the plastic cup
Poor the 3 tablespoons of hot water over the cartridge
Let the ink cartridge soak for about 5 minutes
Squeeze all excess ink from the cartridge, then let soak a little more. repeat until the cartridge is a light color, and the water is dark.

Step 4: Test the Ink

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Using a cotton swab, dip one end into the ink.
tap all excess ink off.
write something on your arm. I did a G for green.
if it you can see it on your arm, then you didn't get enough off the excess ink off. just dab the excess off your arm, and it will be fine.
Go into a dark room, turn on a black light, and watch the message glow!

From this point, you can use the ink for what you want; stamps, cotton swabs, fingers, etc.
Keep reading to see how to make the pen!

Step 5: Making the Pen

Take the Ink Cartridge from earlier, and squeeze it so that excess ink comes out. IT DOES NOT NEED TO BE DRY, JUST DAMP. You should be able to squeeze some out if you try hard.
Re-assemble the pen.
Start with marker tip, and slide it back into place.
Then, put the cartridge into the front part.
push the front piece onto the back piece.
put the cap on.

To use, write with it. to view, look at with UV light.

if you can see the marker when you write, then you need to squeeze more ink out of it.
If the marker isn't writing, then you need more ink in it.

Step 6: Storing the ink

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To store the ink, poor into a small, watertight container. BE SURE ITS WATERTIGHT, UNLESS YOU WANT INK ALL OVER YOUR CARPET. I used a medicine bottle. Also, it might be a good idea to label it.

After your marker stops writing, simply soak it in the ink for a little more, and squeeze the excess out!

Step 7: Other Tips

Picture of Other Tips
the ink works best on skin
Don't where white clothes, and do it somewhere where you can wipe the ink up it it spills.
need a black-light? Home-Depot sells some Eco-bulbs for around $6, Walmart sells a lamp for around $10, and Amazon has a Chauvet Handheld Black light for around $6.
I have 2 of the lamps, one of the bulbs, and one of the handheld ones :) They all work great, especially for the price.

How long does the ink last? And can you change its color?

It lasts until you wash it off, it will not lose its glowing ability. To get a different color just use a different highlighter

AdrienneC6 months ago

How do you recommend storing the ink?

AdrienneC6 months ago

How much water do you need if you are using one of those thick highlighters, and not those thin ones?

Also, to make it better adapted to writing on paper, it helps to put in a few drops of dish soap.

How long does the ink last? And can you change its color?
rimar20003 years ago
Very interesting!
AnaR1 rimar200010 months ago

I totally agree!

Vishvesh1 year ago

can it work without uv, and would it work in a normal room instead of dark room?

sadil31 year ago
Can we take a marker instead of highlighter ???????
If not then can we use the other highlighter its a little bit fat....

Please answer and thnks in advance :)
expertnoobz (author)  sadil31 year ago

It only works with highlighters because of the neon color. But I suppose if the marker is neon it might would work. And yes, any highlighter will work, it doesnt matter the thickness

BluesBayou2 years ago
why do you have one sock on and one sock off?
batonas3 years ago
theres a black light leds, I would put one of those leds in a lighter so it wouldnt look that suspicious, it would be less bright but more stealthy.

heres a list of fuluorescent stuff by wikipedia

laundry detergents containing optical brighteners
Body fluids (those are free)

wolf996 batonas3 years ago
Body fluids (those are free) SICK!!!!!!!!!
Daxuto wolf9963 years ago
In the good way, right?
wolf996 Daxuto2 years ago
I Hope So I Haven't Tried Jizz Yet Though
Daxuto wolf9962 years ago
Honestly, tried with a black light, saw nothing, but I dunno.
wolf996 Daxuto2 years ago
What Using Jizz? It Shows Up Really Well
lukas_tek3 years ago
hey expertnoobz!
i need know one thing
the ink is visible under light of blue led?
expertnoobz (author)  lukas_tek3 years ago
I'm not sure, i don't think it would be. I would test it out, but I don't have any blue LED's at this time.
ok thanks
i will test it out when i go back to my house!
i'm travel and i still conected!
expertnoobz (author)  lukas_tek3 years ago
Cool, let me know what happens!
OT4 expertnoobz3 years ago
I know withought testing it that it does not work with a blue led.