Experiments Using Invisible Ink

Writing secret messages to friends is so much fun!  To be honest, we were about to skip this experiment in our science kit, but after a bit of thought, decided it would be a quick and easy experiment to do before bed.  Quick and easy?  Well, it’s never quick and easy here, as one thing always leads to another!

We decided to try out the method suggested in Usborne’s Science in the Kitchen book.  This method suggests squeezing lemon juice into a bowl, writing on white paper with it, and then developing it with a warm iron.  We didn’t have a lemon on hand, so we used bottled lemon juice, and wrote on pieces of watercolor paper with a q-tip.

Here’s what we found out!

When the lemon juice dried, it was barely visible on the paper (perfect for sending super secret messages).  We developed it with an iron, it showed up a little bit.  Here’s what we ended up with:


Lemon juice

Of course, since we didn’t get a great result, we had to do some research and figure out other methods for making invisible ink.  We found 3 other methods online:

Invisible ink with milk: We did the exact same thing with milk as we did with lemon juice.  The results were similar.  We found that spots of paper that were still damp from the milk got darker when we developed it.



Water and baking soda: We mixed 1/4 cup baking soda with 1/4 cup water.  The downside to this method is that the spots where we wrote were bumpy, and could be read without developing, at the right angle.  When we put it under the iron, the writing was a bit darker and more consistent than the milk and lemon methods


Baking Soda

White crayon and paint: The kids hypothesized that this would be the best method, with the best results.  To do this version of the experiment, all you need to do is write with white crayon on a white piece of paper.  To develop it, you go over the paper with watercolor paint.


White crayon and watercolor paint

Utilizing the white crayon and paint method was clearly the best way to write and develop a secret message!  I think the wheels in their heads are spinning now.  I expect they’ll be asking for paper, envelopes, stamps, and addresses of their friends…

Like I said, one thing always leads to another!

Have you used a different method of writing with invisible ink?  What did you use, and how did it turn out?  



2 Responses to Experiments Using Invisible Ink

  1. Where did you get the white crayon? We tried this using white vinegar as the ink and red cabbage juice as the decoder. It worked really well!!

  2. ScienceAdventureClub

    We just used a white crayon from a regular box of Crayola’s.
    We’ll try the white vinegar and red cabbage juice next!
    Another good experiment would be to see if the message keeps its “potency” after being in the mail for several days.

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