Valentine’s Day Cards – Science Secret Messages

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The 31 Days of Love series continues.. can’t believe that we are already on Day 11! If you are unfamiliar with this series… it is a an annual series for the beginning of the year – when I invite my fellow bloggers from around the world to share the LOVE! Each day, we have a new person share a lovely LOVE post – ideal for Valentine’s Day too of course, but also something you can make all year round with your kids or for yourself! Today we have a great addition to our Valentine’s Day Science Activities!

 Plenty of inspiration for everyone of all ages – whether you are looking for Valentine Crafts for Preschoolers, Valentine Day Treats, Valentine Decorations and Valentine Cards for Kids… browse away and enjoy!

Over to Emma from Science Sparks! Full 31 Days of Love here!

I’m very exciting to be guest posting on Red Ted Art today. I’ve been reading Maggy’s blogs for many years now and love how she can turn the simplest materials into such inspiring crafts, we especially love her toilet roll creations.

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How to Write Secret Messages

Today I’m going to show you how to write secret messages with crayon and lemon/lime juice.

How to Make Invisible Ink

What you need:

  • Half a lemon or lime
  • Water
  • Spoon
  • Bowl
  • Cotton bud or paint brush
  • White paper
  • Oven


Squeeze out the lemon or lime into a bowl and stir.

Dip your paintbrush into the lemon/lime juice and write your message on the paper.

Leave to dry.

To reveal your message you need to apply a source of heat, we found placing in the oven for a few minutes worked the best ( ask an adult to help ).

Can you read your message?

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Extension activities

Think about what would make the perfect invisible ink. Does it need to be invisible before heating?

Try writing messages with lemon and lime juice to see which works the best, what happens if you dilute them with water? Can you make the perfect invisible ink?

How about trying orange juice, milk or vinegar?

Why does this happen?

Lemon and lime juice oxidize (which means they react with oxygen) and turn brown when heated. The invisible ink burns faster than the paper so it turns brown first, allowing you to see it.

Crayon Resist Message

Another great way to write a secret message is to use a white crayon and then colour over the top with different colour crayons to reveal the message.

What you need

  • White paper
  • Crayons
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Write your message on the white paper using the white crayon, you’ll need to press down hard and go over it a couple of times.
Crayon lightly over the top to reveal the message.
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Why does this happen

The thick waxy crayon resists the colouring over the top allowing you to see the message.

If you choose to paint over the message the crayon repels the water based paint, again allowing you to see the message.

Extension Activities

What happens if you use use water based paint instead of crayon to reveal the message.

Would a wax candle work better than white crayon?

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For more fun science activities you can follow Science Sparks on Facebook, Twitter or Pinterest.


Emma gets her inspiration from her three children, the questions they ask and games they play. She spends her days drinking too much coffee, attempting to exercise and blogging as much as possible before school run time.

Other Valentine Science Ideas

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Make a simple stethoscope and listen to your heart beat.

Learn about transpiration and make some pretty coloured flowers.

Entertain your loved one with some science magic.

Fancy some more Valentine’s Day Science Ideas? Take a look at these easy to do and implement projects! LOVE:

STEAM Valentines Activities

Great STEAM Ideas for Valentine’s Day! Nurturing Little Thinkers!

If you are looking for more Valentine’s Day Cards ideas? Here is a list of last year’s 31 Days of Love Cards!

14 Valentine's Day Cards for Kids to Make

Valentines Day Crafts, Activities and Ideas

And here is another version of the Secret Message Valentine’s!