Secret Messages

We all are familiar with ink. It is the fluid inside a pen that allows us to communicate with others through written text. But, most often the communication is not exclusive, that is, anybody who can see the writing on the paper can in principle read the message written on it. Situations are possible when we would not like it to be so, that is when we want to communicate a secret written message. 

Is it possible?

Definitely, science can make it possible. One can make an ink which instead of a dye solution (a coloured solution) has a colourless solution which can be made visible by some method. That is precisely the principle of invisible inks. An invisible ink is a solution which can be used to write with. The written message is either invisible on application or disappears quickly. It can be made visible by some means. The use of invisible ink is a form of steganography, and has been used by spies.

The simplest invisible inks are organic compounds -- vinegar, lemon juice, or even urine -- that are invisible at room temperature but turn brown when heated.

Writing secret messages with an invisible ink is a very simple activity. All you need is some lemon juice (or vinegar), cotton swabs or a paintbrush, a thin white paper and a table lamp with a 100-watt bulb.

Here is the method to do it. 

• Think about what you want to say in your mysterious note! 

• Next, dip the cotton swab or paintbrush (even a toothpick will work) into the lemon juice or vinegar. 

• Write your message on the paper using any of these novel pens. 

• Wait till the liquid dries completely. It should be invisible when it is dry. 

• For your next step, you should ask an adult to help you, because 100-watt light bulbs are very hot. 

Hold the paper over the light bulb (don't stare into the light!), moving it slowly so that all possible parts of the paper are exposed to the heat of the light bulb. 

• The mystery message should appear as the paper heats up.