Glowing Invisible Ink Secret Messages

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Want to learn how to make glowing invisible ink secret messages? I am excited to show you how today! This is such a fun Harry Potter science themed activity to do with kids.

This week I am joining forces with some of my favorite bloggers to bring you a week of Harry Potter STEM activities. You guys are going to love these fun Harry Potter teaching ideas. This week along with my glowing invisible ink secret messages, I have Dry Ice Crystal balls and Arithmancy Math activities for you. Plus, I will be linking to some other awesome Harry Potter STEM activities from the other participants. (Check that out at the end of the post!)

This glowing invisible ink secret message is my version of a marauder’s map. I know it isn’t exactly a map, but you could easily take this activity and make a treasure hunt map or some other hidden secret map with it. My daughter wanted to do a series of clues with ours to lead her brother on a hunt around out yard.

Watch it in action here:

Did you know that laundry detergent glows? Cool, right?  We have tried a few different invisible ink experiments to decide which is our favorite. This glowing invisible ink is the best one we have tried. All you need is laundry soap and a small paint brush or q-tip.

Water the soap down just a tiny bit.

We used a very fine paint brush to write the message. A smaller tip works best so you can write the letters smaller. Once it is written, it takes a bit of time to dry out, especially if it is written thick.

When it is dry, you do see spots where the soap is, so it is not perfectly invisible, but is nearly impossible to read it without the black light.

Our message starts with ‘I solemnly sear that I am up to no good,” because that is the phrase used on the Marauder’s map! Then my daughter said to meet her under the whomping willow tree. 🙂 From there she led her brother on another series of clues.

We have a little UV flashlight that we used to reveal the messages. This was perfect, but any black light or UV light will do!

The Science Behind the Glowing Invisible Ink:

Why does it glow?

Laundry soap has something added to it called phosphors. This helps to make clothes appear brighter in the sunlight. A phosphor is something that glows under a black light. When they are exposed to the Ultra violet light they absorb the light and remit some of it back. It is also called fluorescence.

Download the blank map now!

See more Harry Potter Themed Activities:

Harry Potter STEM: Arithmancy Math
Harry Potter Dry Ice Crystal Ball Experiment
Harry Potter Escape Room for Teaching

Check out the rest of the awesome Harry Potter STEM ideas by hopping over to Babble Dabble Do.

Also posted today:
How to make a Magic Wand from Babble Dabble Do
Troll Bogeys (Magnetic Slime) from STEAM Powered Family