Cranberry Spy Ink Science Experiment

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You know that look when a science experiment works and your kids’ eyes go huge, like they just did magic? That’s this cranberry spy ink experiment.

Kids write invisible messages with baking soda water, then paint over them with homemade cranberry ink and watch the secret appear.

Ages 4 and up
Time 30 minutes
Science Acids, bases, pH
Adult help Stove and blender
Cranberry spy ink supplies

How to Do the Cranberry Spy Ink Experiment

Green tray setup showing cranberry juice, baking soda solution, Q-tips, paintbrush, and blank paper ready for the experiment.

Crawling Colors Science Experiment

Get the printable

1 cup fresh or frozen cranberries

1/2 cup water, plus 1/2 cup for the baking soda solution

2 tablespoons baking soda

Cotton swabs and a paintbrush

White cardstock

Saucepan, blender and strainer

Simmer the cranberries

Simmer the cranberries and 1/2 cup water for 8 to 10 minutes, until most berries burst.

Simmering cranberries

Blend

Let it cool a few minutes, then blend until smooth.

Cranberries being blended with an immersion blender in a glass bowl, creating a thick red pulp.

Strain

Press it through a fine strainer to get a thin red ink. Add a splash of water if it’s thick.

Smooth cranberry juice mixture in a glass bowl with a red spoon resting inside.

Make invisible ink

Stir 2 tablespoons baking soda into 1/2 cup warm water.

Spoon stirring the white baking soda solution in a clear glass bowl.

Write the message

Dip a cotton swab in the baking soda water and write or draw on cardstock. Let it dry completely.

Child using a Q-tip dipped in baking soda solution to draw a house on white paper.

Reveal it

Paint the cranberry ink over the paper and watch the message appear in a darker purple-blue.

Child painting cranberry juice over the paper to reveal a hidden gingerbread man and house drawn in invisible ink.

Shortcut and safety

Short on time? 100% cranberry juice works too, though the color change is lighter. A grown-up should handle the stove and hot cranberries.

How Cranberry Spy Ink Works

Cranberries are full of natural pigments called anthocyanins. They change color depending on whether something is an acid or a base.

Cranberry juice is acidic, so it’s red. Baking soda is a base. Where the cranberry ink touches the baking soda, the pigment shifts to purple or blue-gray, revealing the message.

Try the fizzing cranberry experiment next to see the color change in a jar.

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Love easy kitchen science? Try our Skittles experiment.

The science experiment includes

  • Step-by-step directions
  • Prediction and observation sheets
  • Simple science explanation
  • Instant PDF download, nothing is shipped

Perfect for

  • Science centers
  • Homeschool
  • Holiday science
  • Ages 4 and up

Cranberry Spy Ink FAQ

How does cranberry spy ink work?

Cranberry pigments change color in a base. The baking soda writing turns purple-blue when cranberry ink touches it.

Can I use cranberry juice?

Yes, 100% cranberry juice works, but the color change is lighter.

What paper works best?

White cardstock, since it doesn’t wrinkle as much.

What age is this experiment for?

About 4 and up, with an adult for the stove.

More Cranberry Activities

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From families like yours

Did you try it? Tell us how it went!

We love seeing these activities out in the wild: the lumpy letters, the snack breaks, the proud “I made a B!” moments. Leave a star rating, tell other parents what worked (and what totally didn’t), and add a photo of your setup if you’d like.

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Stephanie Oswald, early childhood intervention specialist and creator of Parenting Chaos

Hi, I’m Stephanie!

I’m an early childhood intervention specialist and the mom behind Parenting Chaos. I share simple, hands-on activities that help little ones learn through play. Coffee addict, nature junkie and kid at heart.

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