How to make invisible ink

Invisible ink is any substance that you can use to write a message that is invisible until the ink is revealed. You use the ink by writing your message with it using a cotton swab, dampened finger, fountain pen, or toothpick.

MATERIALS:-

1. Highlighter (I got a pack of 4 different colors for only $1)
2. 1 cup (plastic works best, so you don't have to worry about washing it out)                     
3. 3 Tablespoons hot water
4. Cotton swab
5. Pliers

METHODS:-

Step 1:Take Apart the Highlighter

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 2: Extract the Ink

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 3: 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 or UV light, and watch the message glow!