Friday 12 April 2013

Science: Invisible Ink!

I'm going through four different types of invisible ink.  These three experiments are simple experiments fun for most ages. 

What you will need before you start:

· Test tubes
· lemon juice
· iron sulfate
· copper sulfate
· ammonium chloride
· a measuring beaker
· a beaker
· a paintbrush or a something similar like a cotton bud stick
· non glossy paper
· a hairdryer or iron
· an adult
· a shallow dish
· Iodine

Invisible ink number 1

This is is a safe experiment for any age to try pretty independently.
For this experiment all you will need is:
  • a piece of non glossy paper
  • a paintbrush or a cotton bud
  • lemon juice 
  • A hair dryer or iron


With your paintbrush write a secret message on your piece of paper. 


Heat up the paper with whichever method you choose, the hair dryer or iron, but be careful not to burn it - you may need your adult at this point.

What colour does the invisible writing go?

Invisible ink number 2
Now to try a different type of invisible ink. 
You will need:
  • Iron Sulphate
  • Water
  • A shallow dish
  • Coffee filter Paper
  • A hair dryer or iron
  • A test tube


Put a 1/8 of a teaspoon of iron sulfate in a test tube and add about 1cm of water to it. 
Pour it out into a shallow dish and then, with your paintbrush, write another secret message. 
Allow it to dry a little and then again heat the paper. 
What colour is the writing now?

Invisible ink number 3
I love this one, you will have to try it out to see why...
You will need:
  • A test tube
  • Copper sulphate
  • Ammonium chloride
  • Water
  • Non glossy paper or coffee filter paper
  • A shallow dish
  • A paintbrush or cotton bud


Add 1/8 of a teaspoon of Copper sulfate and 1/8 of a teaspoon of ammonium chloride to 1cm of water in a test tube and mix well and carefully. 


Pour in into a shallow dish and with a paint brush write another secret message on another piece of non-glossy paper. 

It's a little blue right?  It works extra well if you use blue paper for this experiment


Now heat it...  What colour does it go?  Cool isn't it!

Invisible ink number 4

I advise this one for older children, preteens and teenagers.
This is the last of my invisible inks, to make it you will have to prepare your own iodine solution for.  You must be careful with this solution you make and if you want to dispose of it dilute it with plenty of water and get rid of it down the sink.

Now for the invisible ink experiment using the developer, the iodine solution - you will have to make your own so go to my post how to make an Iodine solution and make some up first.
You will need:


In a cup mix a teaspoon of cornflour with about a 1/3 of a cup full of water and stir until it is all mixed in.  This will be our starch solution. 


With a paintbrush write another secret message on filter paper.  Let the writing dry completely. 


Put 30ml of water in the measuring jug and add 10 drops of the iodine solution to the water pour this solution on a plate and then drop your filter paper into the solution. 

What happens?  What colour is the writing.

This reaction occurs for the same reason as the iodine clock.  It is the reaction between the iodine and starch.   If you want to to the iodine clock experiment you'll find it here.


  1. Fantastic experiment - I've just discovered you via the Ipswich Home Edders facebook group

    1. Thanks for your kind comment! :D There are many more on my science page: