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Tuesday, November 8, 2011

Invisible Ink, easy to write hard to read

Secret messages, they love it! To be able to write something on a piece of paper that no one can read is amazing.

Today we are going to see 3 ways to write something that no one can read but you, you will doubt about which the paper sheet was used.

Invisible ink with baking soda
We already used baking soda on several demonstrations and fun games, today we will use it to write…

We will need:

  • 1 cup,
  • 60ml of water,
  • The same amount of sodium bicarbonate,
  • toothpicks,
  • paper. 
How to:
  1. Measure 60ml of water;
  2. Pour water into the cup;
  3. Measure 60 ml of sodium bicarbonate, this is solid, so it may seem strange measure in ml, but do it :);
  4. Mix baking soda in water;
  5. Mix it until the solution is homogenized;
  6. Get your paper, and write your message with the toothpick.
How do you read it? 
Spread grape juice over the sheet; use a sponge or a brush. 
NOTE: the grape juice leaves stain.


Sodium bicarbonate is a chemical compound that has a basic pH, the grape juice is acid, and the reaction between the two rise to a third colour, visible to the naked eye.

Invisible ink with milk

We need:

  • Milk,
  • Toothpick,
  • Paper sheet.
How to:
  1. Put some milk in a bowl;
  2. With the toothpick or brush to write the secret message;
  3. Let dry completely.
How do you read it? 
There are several hypotheses; all of them require a heat source, and the supervision of an adult.
You can iron the sheet, place a cloth between the iron and the message so the iron dot get dirt, you can heat the sheet next to a lamp, be careful so it doesn’t get on fire, or, and finally, you can use the stove.


Milk is an organic product, and burns at a slower speed than the paper. When you heat the paper, the milk is leaves a brownish colour and you can read the message in the white sheet.

Invisible ink with lemon:

We need:

  • Lemon juice,
  • Toothpick,
  • Paper sheet.
How to:
  1. Place a little lemon juice on a plate;
  2. With the toothpick or brush write the secret message;
  3. Let dry completely.
How do you read it? 
As in the the milk ink, you can pass the iron sheet, the sheet can heat with a lamp, or you can use the stove, either of these alternatives requires adult supervision. There is another way to see the message by putting salt on the sheet, in this case wait about 60sec and clean the salt, then, and carefully pass a crayon over it.


For the same reason that points to the use of milk

In addition to these dyes, we can use other products such as white wine, vinegar, other fruit ...

You can make this demonstration in an experiment using other liquids that you think that might work.
Register which works best and what are the safest methods to read, do not forget that the aim is to get a top-secret message without being caught.

Et voila!
Nobody will notice that blank sheet on the table.


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