How to Make Invisible Ink
Elsewhere we have talked about writing secret codes. What better way to write your secret code than with invisible ink?
It will disappear soon after you write it down, making it meaningless to enemy agents and other dubious characters whom you may not wish to read it. Spies and others have been using invisible ink for centuries.
Give it a try. The ingredients are to be found in most households, but the secrets are entirely yours.
- An ounce or two of lemon juice or vinegar in a cup or bowl
- cotton swabs or paintbrush
- thin white paper
- a lamp with a 100-watt bulb
- 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 a message on the paper.
- Wait for it to dry completely. It should be invisible when it dries.
- For this 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.
What Happened:
Lemon juice and vinegar have acidic properties. The acid weakens the paper, remaining potent even after it dries. When the paper is held near a heat source, the lemon juice, or vinegar-treated parts of the paper burn more quickly than the non-treated portions of the paper. That’s why they turn brown!
