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Saturday Science Experiment: Spies and CSIs

Looking for a weekend project? Here are three activities that little spies and detectives can do with regular household items. Write secret messages and reveal them easily- no lemon juice or open flames! Then create a fingerprint database of the members of your household with very little mess.

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Spy project #1: Invisible messages with wax and watercolors

Supplies: scrap paper, white crayons, watercolors, paintbrush, an optional smock

Procedure: On a piece of paper, draw a secret message or picture with the white crayon. To reveal the message, paint over it with watercolor paint. Voila! 

The science: The wax from the crayon creates a barrier that keeps the paint from adhering to that part of the paper. In art this is a method called wax resist. You may have used this technique to create designs on dyed Easter eggs. 


Spy project #2: Invisible ink with baking soda and juice

Supplies: scrap paper, baking soda, water, dark colored juice (we used grape), paintbrush, small sponge or cotton swabs, an optional smock

Procedure: Mix up the water and baking soda in a 1:1 ratio. Mine was 2 Tbl water and 2 Tbl baking soda. Mix well, then using a paintbrush, paint your secret message on a paper. Let the paper dry completely. To reveal the secret message, dip a cotton swap or a sponge in the dark colored juice (we used grape, but cranberry would also be a good option) then gently "paint" a generous amount onto your message. It will reappear! Note, this is one of those "self-destructing" messages, once it dries, your message won't be very clear anymore.

The science: There are pigments in the juice called anthocyanins. These give the juice its color and react with the baking soda. Anthocyanins work as a pH indicator, just like a piece of litmus or pH paper. pH is the scale of acids and bases. Since baking soda is a base, the pigments react and change color, hence your message is revealed! A similar pH experiment can be found in my post: "Saturday Science Experiment: Science with Christmas Leftovers" 


Crime Scene Investigator Project: Fingerprint database

Supplies: pencil, pencil sharpener, scrap paper, scotch tape, your fingers

Procedure: Using a freshly sharpened pencil, color a dark splotch on a piece of scrap paper. Rub your finger on the pencil splotch. Using a piece of tape, "lift" the print off of your finger. Place it on your database sheet. You can create a fingerprint database for the whole household!

The science: As we all know, everyone's fingerprint patterns are different. The skin on the fingertips is ridged, which creates a specific pattern that can be left behind on certain surfaces. There are three main types of fingerprint patterns- loops, whorls and arches. Once you have created your database, you can compare the prints for these patterns. Learn more about these patterns in depth here.


Did you try any of these activities? Share your experience by commenting below, or e-mailing me at

Are you looking for other easy at-home science projects? Check out my "Saturday Science Experiment" page. You'll also find some great quick science experiments for kids here. Happy Experimenting!


  1. This was much easier than trying to use powder and lift off the finger print and transfer it to black paper! This is a win for Kid's Camp!

    1. Glad to hear of your success! I found this method by accident and it certainly has been easier for kids to do successfully and less messy, especially for little hands! Thanks for stopping by the blog!

  2. Some great ideas. Thanks. I will be using this with my class next term