“Secret” Messages

“Secret” Messages

Incorporate a bit of science and use chemistry to write a secret message this Valentine’s Day, or any day!

Two options are presented below.  One takes advantage of a chemical reaction between two substances (baking soda and lemon juice).  The other takes advantage of the reaction between lemon juice and heat.


  • white paper
  • baking soda
  • lemon juice
  • water
  • paint brush or Q-tip
  • heat source (light bulb, hair dryer)
  • small spray bottle (optional)

Procedure (Baking Soda Message):

1)  Combine approximately 3 teaspoons of baking soda with 2 teaspoons of water and use a paintbrush or Q-tip to write a message with the baking soda “paint” on the white paper.

2)  Let it dry and brush any excess baking soda off the paper.

3)  To reveal the secret message, spray lemon juice on the message.

How It Works:

The lemon juice acts as a pH indicator that changes color when it reacts with the sodium bicarbonate of baking soda, which is a base.

Procedure (Lemon Juice Message):

1) Use a paintbrush or Q-tip to write a lemon juice message on white paper.  Allow the message to dry.

2) To reveal the message, expose the paper to heat.

How It Works:

Lemon juice is an organic substance and therefore contains carbon molecules that oxidize and turn brown when exposed to air.  However, because the lemon juice used to write the secret message is diluted by water, the oxidation of the carbon molecules from the lemon juice that are absorbed by the paper are not noticeable until the paper is exposed to heat, which causes some of the chemical bonds to break down, freeing the carbon.