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  • Writer's pictureSuzie Olsen

Science Experiment: Invisible Ink for #BackToHogwarts Day

Updated: Oct 23, 2018

I have learned that September 1 is Back To Hogwarts Day! If you're not in the know about the Harry Potter books, Hogwarts School of Witchcraft and Wizardry is the school attended by none other than Harry Potter himself. While I do adore the book series, I'm tame in Harry Potterhead fandom compared to others. But when one learns of Back To Hogwarts Day, it is hard not to have a tie-in to your blog regardless of your level of Potterheaded-ness. Also science is magic. So in honor of Back to Hogwarts Day, I am going to be doing various Harry Potter inspired posts throughout the month of September!

For STEM Spark's first Harry Potter inspired post, I thought of the science experiment invisible ink! What better way to pay tribute to the magic of Harry Potter than with science that is invisible until the magic (ink) is used?! Invisible ink is a not-so-subtle nod to the Marauder's Map in the book series -- the map is invisible to most users unless the magic phrase "I solemnly swear that I am up to no good" is uttered. And sometimes in science, you have to break the rules to make new discoveries (in a positive kind of way, not the negative I-want-to-destroy-everything-Voldermort kind of way). So without further ado, let's solemnly swear that we are up to no good in science and make some secret messages with invisible ink!

You'll Need:

Tsp of Baking Soda

2 Tsp of Water

1/4 Cup of Grape Juice or Blue Kool-Aid or Lemon Juice

Cups to Hold Liquid

Plain White Paper

Paint Brushes


1) To make the ink, mix the tsp of baking soda with 2 tsp of water in a cup. Stir until evenly mixed. Note: The baking soda may not fully dissolve, so you may have to stir the ink mixture on occasion.

2) In another cup, pour about 1/4 cup of either grape juice, blue Kool-Aid or lemon juice.

3) Dip a paint brush into the baking soda ink and write a (secret, shhh) message on the plain white paper. You can use other types of paper, but plain white hides the baking soda ink best.

4) Let the ink dry for about 5 minutes. While you wait, watch a clip of Harry receiving the Marauder's Map from Fred and George (the twins are my second and third favorite characters; Hermione is my number one favorite character because she was smart and brave, everything a STEM girl needs!): Harry Receives Marauder's Map

5) Now for the reveal! Lightly dip another paint brush into the juice and lightly rub it over the piece of paper. The key here is that less (juice) is more.

So, I chose the method of invisible ink that is better suited for toddlers and preschoolers (I even think you could do this method with a one year old), but there is another method with heat and lemon juice. I wasn't so concerned about the lemon juice and my three year old (oh god, you squirted it in my eye, I take that back! Also why safety goggles are good), but the heat part. I just didn't even want to chance a three year old using a stove or hot light bulb, but if you have an older child/are an older child, I recommend checking out the lemon juice and heat method. Check it out at the Scientific American. Happy science experimenting like you're a wizard! And stay tuned for more Harry Potter STEM fun!

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