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

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

-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

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

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

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

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.

2 People Made This Project!


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33 Discussions


2 years ago

Didn't really work, sorry


2 years ago

Are these pens washable? If I wrote on t-shirts with them and then put the t-shirts in the washing machine - would the ink come off completely? TIA


2 years ago

Can I make invisible ink using a black stamper pad.


3 years ago

I did it for 10 minutes, and the cartridge is still orange with a little yellow at the tips. When i reassembled the highlighter, it still wrote visibly. I have to almost not press at all to make it invisible, but then it does not show up on my black light. Any tips?


3 years ago

The reason this works is because the highlighter ingredients are fluorescent, so it would have to be a highlighter, and a blacklight. If you want to do this with any old marker, do this, but wash out ALL the ink. You can throw this away. Then saturate the ink cartridge with tonic water. The quinine in the water fluoresces, and should allow you to produce actually invisible messages. This instructable one would still be a little green. I havent tried using it to write messages, so I can't 100% confirm that the concentration of the quinine is high enough to be visible, but I assume it would be. I suppose you could let the mixture evaporate out some water to concentrate it more, but don't boil it, you'll just denature the quinine.


3 years ago

can u use a marker instead and does it have to be a black light can it be blue


3 years ago

is it important to use a black light cant it appear in dark

Just to be clear, if I go down to Walmart and buy a Halloween black light-bulb, would that work? I've tried another set of "Halloween black lights" and they didn't seem to make the ink show up. Thanks!

1 reply

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


4 years ago on Introduction

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.


4 years ago

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


4 years ago on Introduction

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


5 years ago on Introduction

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 :)

1 reply

Reply 5 years ago on Introduction

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