Make Invisible Handprints

Watch a red handprint appear on blank paper when you brush turmeric ink across it.

 

Materials you'll need

• baking soda
• warm water
• measuring cup
• cup
• shallow bowl
• white paper
• ground turmeric
• alcohol-based hand sanitizer
• small cup
• paintbrush
• paper towels

 

Step-by-step tutorial

Step 1: Scoop baking soda into a shallow bowl, then pour in enough warm water to make a thin, milky mixture. Stir until most of the baking soda dissolves.

Step 2: Dip your whole hand into the mixture and press it firmly onto a sheet of white paper. Make as many prints as you like, dipping your hand again each time.

Step 3: Let the paper dry completely. As the water evaporates, the prints fade until the paper looks blank again.

Step 4: Shake ground turmeric into a small cup and add a few pumps of hand sanitizer. Stir with your paintbrush until you have a smooth yellow ink. Hand sanitizer is alcohol-based, so keep it away from heat and flames and use it with a grown-up.

Step 5: Spread paper towels across your work surface and lay the dried paper on top. Turmeric stains, so this keeps the mess contained.

Step 6: Paint the turmeric ink across the paper in long strokes. Everywhere your hand touched turns deep red, and your hidden prints appear.

Learn more

Turmeric gets its yellow color from curcumin, a natural pH indicator. That means it changes color depending on whether it meets an acid or a base. Curcumin stays yellow on plain paper, but baking soda dissolved in water is a mild base, so wherever your hand pressed down, the dried baking soda turns the curcumin deep red. Hand sanitizer does the other half of the job, because curcumin barely dissolves in water but dissolves easily in alcohol, which is what turns the spice into paintable ink.

If this project was a hit, Bubbling Cauldron takes acid-base chemistry further with a witch's cauldron that bubbles over when kids pump water onto citric acid and colored baking soda.