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How to Write a Secret Message in Milk

Learn how to write a secret message in milk with the instructions in this Howcast science project video.


Have you guys ever had a message or a secret that you wanted to share, but you were so afraid that if you said it on the phone, mommy could hear you or if you said it in school one of your friends would hear you? Well, what if I showed you how to tell that message by creating invisible ink? And I know what you're thinking, you need really expensive materials.

Actually, no. At lunch when you're drinking milk, take the milk, because that's the key ingredient to making this invisible ink.Milk, that's right. And you know what else I need? A Q-Tip, what you clean your ears with is what I'm going to write with. Step one I'm going to take this Q-Tip, I'm going to dip it in the milk. Now I'm going to write a note. I'm not going to tell you what I'm writing, okay?

So watch this. As I dip the Q-Tip into the milk, I write on the paper and the milk is being absorbed by the paper. Absorb is when it's able to suck it up. Now what happens is the milk eventually will evaporate, which means the liquid is going to turn into a gas.

But you want to know the cool part? Whole milk, and by the way, do not do this with skim milk, whole milk has fat in it. Fat does not evaporate. The milk will. The fat will stay. Now you really need to wait a half hour for this to try to do the second part.

So I already did this. The same method that's here, is here. Now how do you get to see the message? It's invisible. Part two, take two pencils. Now you could use pencil tips and rub them together or you can get a piece of sandpaper.

Sandpaper is extremely rough and when you rub two things together it creates friction, and the graphite from the pencil rubs off. So it kind of looks like it's snowing. Ready? Now as you rub, the graphite from the pencil starts to slowly fall on to the paper and you're going to get really upset, because you're going to say, "Wait a second. This isn't working. The message isn't there."

Carmelo, this experiment is a failure. Stinka-rooney. Actually, want to see something really cool? Take your finger. As I start to rub the graphite that's on the paper across the paper, it's going to find the fat from the milk and stick to it, and the message that I wrote starts to magically appear or in science, scientifically appear.

Ready? Now I wrote a really important message for you kids, okay? Because it's true and you'll admit that it's true. Do you know what the message is? Let's see. Now you saw the paper there a minute ago. You weren't able to see anything, but right now my message is to you kids, "Kids have smelly feet."

And you know it's true. I just made invisible ink using nothing but milk and Q-Tips and a pencil. Go make a note. You can make something fun like this, give it to daddy, give it to mommy and have them see how important you are and how amazing science truly is. Go have fun.

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