Sometimes you get a happy accident, such happened when I went to the library to get some dog books, and found a book mentioning invisible ink using lemon juice. I knew this could turn into all sorts of fun lessons. This started off as a science lesson as we learned about chemistry and how heat changes the lemon juice. We learned about this again when we studied the American Revolution and George Washington using invisible ink. Let’s dive in and learn about invisible ink
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The inspiration for our invisible ink lesson
So, as I mentioned yesterday, we read Invisible Inc Mystery of the Missing Dog. In the book, they write secret messages to each other using invisible ink from lemon juice, and they used all sorts of things to reveal the ink. They used the steam from a hot dog to reveal it and I forget what all else, so that got me curious if this would really work.
Materials needed for the invisible ink lesson:
Hypothesis: if you draw with the juice when it is exposed to heat it will turn brown and reveal your secret message. We’re going to see which way works best.
Oh, and all documentary pictures taken for this experiment were taken by my kids today. So, they’re sometimes interesting…..
Results of our invisible ink lesson
1. Cut your lemons in half and squeeze all the juice out of them into a bowl. Honestly, we could have done this with one lemon, but each kid wanted their own lemon.
2. Take some pictures of your head. While you’re at it why not take pictures of the light and the wall?
3. Paint your picture. While you’re at it make sure to completely saturate the paper. I’m sure it’s a better message if the paper is completely soaked.
4. First we tried it over the candle. Sorry for the blurry photo. It worked somewhat. I’m beginning to think it might have worked better if the papers were slightly dryer. It would reveal the ink for the area directly over the flame, but that’s all.
5. Next we tried it over the burner on our stove. Very important, to make sure the adult is doing this. I’m sure that goes without saying, but the flame is very hot, and the other important thing is to make sure the flame is on low. You have to hold it over for a little bit and it does get hot very quickly. This worked best.
6. On the last ones we tried the hairdryer. According to National Treasure (and I tried to find a clip of this from the movie, but no luck) if you blow a hairdryer over it then the picture will be revealed. Well, maybe I don’t have a hot enough hairdryer because all it did was dry out the ink. Again, I’m wondering if the paper was less saturated if that would work better.
The end result of our invisible ink lesson
Here’s Batman’s picture. Can you tell it’s a space guy with a gun fighting a monster? Good, I could too.
This is either Superman’s or Princess’, I’m not sure which. They both went for the cover-the-page approach on most of theirs. Though I was amused as Superman sat there explaining that his lemon juice was rain that was coming down……
Why lemon juice invisible ink works
For a scientific explanation and for some other invisible inks go here. I really wanted to find a video, but it just wasn’t happening. (Future Ticia 2020 was able to find a video)
For a more in-depth discussion, including some more historical context, check out this video.