EC loves anything that could be remotely spy related, so when I suggested that we write our Valentine’s cards in invisible ink, he jumped at the chance.
Before we go any further I will say that although writing the cards is fine, reading them requires ADULT SUPERVISION. To activate the ink you need to place the letter next to a heat source. I tried a light bulb and a hair dryer but they didn’t work for me. What really worked was holding the paper above a candle. As you can see, this could be a potential fire hazard. So make sure that you either do this part outside or with water nearby. The first note I practiced on went up in flames.
Now that we have that out of the way, let’s get down to business.
You will need:
- Card stock in black and red
- White paper
- ½ a lemon
- Small bowl
- Ear buds
To write the secret love note you will need to squeeze half a lemon into a small bowl and add a few drops of water.
Cut some plain white paper into small notes. I tried with a variety of different types and coloured paper but none of them worked.
Dip an ear bud into your lemon juice and use it to write, or draw, your love note.
Then leave it to dry.
While waiting for it to dry it’s time to make your cards.
First cut out a heart shape from the red card.
Then cut out a black square that is big enough to fit the heart in it.
Add a little bit of glue to the outside corners of the heart and stick it down. You don’t want to glue the top part of the heart down as this is going to make a pouch for the letter to sit it.
Once the letter has dried roll it up and place it into the pouch on the card.
To complete it I put instructions and a warning on the back of the card, which is a first for a Valentine’s card.
To read the card/ Science behind it
The lemon juice is an organic substance that oxidises and turns brown when it comes into contact with heat. You can apparently do this with a hair dryer, light bulb or even an iron, but I didn’t have any luck with those. I used a candle. The trick is to get the paper close enough without actually touching the flame. I held it over for a few seconds at a time and then removed. It was pretty cool to watch the message suddenly appear like magic.
Pin for later: