How To Make Invisible Ink - Baking Soda

Easy Baking Soda Invisible Ink Instructions

Some types of invisible ink require special lights to reveal the message. Baking soda invisible ink messages are easily revealed using heat or grape juice.
Some types of invisible ink require special lights to reveal the message. Baking soda invisible ink messages are easily revealed using heat or grape juice. Bettmann / Getty Images

These are instructions for making non-toxic invisible ink using baking soda (sodium bicarbonate). The advantages of using baking soda are that it's safe (even for kids), simple to use, and readily available.

Difficulty: Easy

Time Required: A Few Minutes

Invisible Ink Ingredients

  • Baking Soda
  • Paper
  • Water
  • Light Bulb (heat source)
  • Paintbrush or Swab
  • Measuring Cup
  • Purple Grape Juice (optional)

Make and Use the Ink

  1. There are at least two methods to use baking soda as an invisible ink. Mix equal parts water and baking soda.
  1. Use a cotton swab, toothpick, or paintbrush to write a message onto white paper, using the baking soda solution as 'ink'.
  2. Allow the ink to dry.
  3. One way to read the message is to hold the paper up to a heat source, such as a light bulb. You can also heat the paper by ironing it. The baking soda will cause the writing in the paper to turn brown.
  4. A second method to read the message is to paint over the paper with purple grape juice. The message will appear in a different color. The grape juice acts as a pH indicator that changes color when it reacts with the sodium bicarbonate of baking soda, which is a base.

Tips for Success

  1. If you are using the heating method, avoid igniting the paper - don't use a halogen bulb.
  2. Baking soda and grape juice react with each other in an acid-base reaction, producing a color change in the paper.
  3. The baking soda mixture can also be used more diluted, with one part baking soda to two parts water.
  1. Grape juice concentrate results in a more visible color change than regular grape juice.

How It Works

Writing a secret message in baking soda solution slightly disrupts the cellulose fibers in paper, damaging the surface. When heat is applied, the shorter, exposed ends of the fibers darken and burn before the undamaged sections of paper.

If you apply too much heat, there's a risk of igniting the paper. For this reason, it's best to use either the grape juice chemical reaction or else apply a gentle, controllable heat source.