Invisible Ink

Invisible Ink



This project is half art, half science, and all fun! Just write a message or draw a picture in lemon juice or baking soda invisible ink, then reveal the hidden message by rubbing the paper with flowers. The color of the flower smear changes wherever you painted with the invisible ink. In fact, different flowers create different color changes, so it's the perfect experiment to try with a mixed bouquet of flowers, or with flowers from a garden.


The secret here is that the flowers act as pH indicators, changing color in an acid or a base. By using both an acid (lemon juice) and a base (baking soda), you can create a painting that reveals two different colors when you rub the flowers over it. We had a great time experimenting with our flowers. Definitely worth the sacrifice of a bouquet!

Ages:
3 - 8
Est. Time:
1-2 hours

How we did it:

Materials List

  1. fresh flowers
  2. paper
  3. paintbrush (cotton swab)
  4. bowls
  5. lemon juice
  6. baking soda
  7. water
  1. Gather the materials to make your secret flower messages. 

  2. Start by making your secret message juice. In one small bowl, pour a little bit of lemon juice. In another small bowl, mix up a big scoop of baking soda with just enough water to make it a liquid. You want a lot of baking soda to get a good color-changing effect.

  3. Using a paintbrush or cotton swab, paint your secret message or drawing on the paper. You can just draw a picture, or write a secret note. Or, write a riddle in pen, and then write the answer in the invisible ink.


    You can use both the lemon juice and the baking soda in the same drawing if you like. The lemon juice and baking soda will turn different colors.  

  4. Let the paper dry for at least an hour or so, until all the water has evaporated and your message is invisible.

  5. When you're ready to reveal your secret, rub a flower over the surface of the paper. The smudge will change colors wherever you painted with the lemon juice or baking soda.

  6. Rub over all your painted papers with the flowers to reveal your messages and drawings.


    Lemon juice and baking soda aren't the only liquids that work. Test out other liquids (like vinegar) and see what you can find.