We love fun kids’ science and this easy rainbow jar activity is one of our all-time FAVORITES! With just a few common household ingredients like dish soap and honey, little scientists can actually pour a rainbow in a jar. There’s no need for any magic – just 100% kid-friendly science.

Follow the simple step-by-step below and then grab 30 more easy-to-follow science experiments kids will beg to repeat (plus a no prep science journal to keep track of their results!) in our shop!

Getting Ready

This project requires quite a few supplies, but most of them are probably things you already have in your pantry.

To get ready for the science activity, I grabbed my materials:

  • A tall, see-through container (I used a clean mason jar.)
  • Honey
  • Light corn syrup
  • Dish soap (either blue like Dawn or green like Palmolive)
  • Olive oil
  • Rubbing alcohol
  • Water
  • Food coloring
  • A dropper

I also grabbed two identical containers and some marbles so that I could give my son a brief explanation about density.

The Science Behind It

As always, my son was really excited when I told him we were going to do some kids’ science with a rainbow jar! Before we jumped into the project though, I wanted him to understand what was about to happen, so I decided to introduce him to the concept of density first.

I explained that different liquids have different weights.

“Everything is made up of teeny tiny things called molecules,” I said.  “Some of these liquids have a lot of molecules in them and some of them have only a few.”

I showed him two containers that were the same size.  One had a bunch of marbles in it, one only had six.

Science for Kids Rainbow Jar

I had my son hold the two containers and asked him which one was heavier.

“The one with more marbles,” he said.   I explained that it was the same with our liquids — the ones with more “marbles” (molecules) were heavier and would stay at the bottom of the jar.

St. Patrick's Day Science Experiment for Kids: Rainbow Jar.

Pour a Rainbow in a Jar

Now it was time to make our rainbow jar!  First, my son poured in the honey, being sure to pour it into the middle of our container. He was careful not to let it touch the sides.

Next, he poured in the corn syrup. (We’d colored it purple using the food coloring.) Again, my son poured it into the middle of the container, not touching the sides.

The dish soap came next.

Make a Rainbow in a Jar

We poured in regular water that we colored blue. (If you’re using blue dish soap, obviously color your water something different. Again, in the middle, in the middle!)

The olive oil went in the rainbow jar next. Do you know what I’m going to say? That’s right, we poured it in the middle! Also, I recommend pouring a fairly thick layer of oil – it will come in handy for the next step.

Last but not least was the rubbing alcohol.  We colored it red – that in itself is a cool peek at different densities because the food coloring just sits at the bottom of the alcohol when you first drop it in.  BUT WAIT! DON’T POUR IT IN THE MIDDLE!

Rainbow Jar 3

This is where the dropper comes in.  If you pour the alcohol straight in, it’ll probably pick up the blue food coloring you used in the water and your rainbow will be ruined.

We found the best way to add it was dropping the alcohol along the side of the container using a dropper.  The key was not “breaking through” the oil layer into the blue water layer beneath it – that’s why I suggested putting a thick layer of oil.

How to Make a Rainbow in a Jar

Our rainbow was done!  We held it up carefully to the light, making sure not to shake it, and admired our beautiful creation.

More Simple Science Kids Will Love

Inspire kids to LOVE science with 30 more jaw-dropping experiments they’ll beg to repeat!

Grab 30 easy-to-follow science experiments kids will beg to repeat (plus a no prep science journal to keep track of their results!) in our shop!

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155 Comments

  1. Are there any standards for elementary school grades that would go with the activity? I am actually using this activity for my science course I am taking this summer and am making a lesson plan based on it.

  2. After making the rainbow jar, for how long can you keep it?
    My guess is that there are fairly stable at room temp, but I’m not sure.

  3. would you have another suggestion to use in place of the corn syrup?

  4. We do something similar in my 8th grade science classroom. Yes you can shake it up (the soap will get foamy), yes you can let the liquids touch the sides, and yes it is stable at room temp. Ditto to the please don’t over simplify to the point of confusing weight with density.

    A better way to explain this is that it is all about floating and sinking. You can push a low density object like a beach ball to the bottom of a swimming pool but it will float up to the surface because it is less dense than the water. Exactly the same thing happens if you pour the less dense liquids first. In my class each kid pours a small amount of liquid in so we don’t have any layers to start and we see them form. ***food coloring has its own density so it may not travel with the layer you started it in or it may bleed between layers***

  5. Thank you so much!! I used this for a science project the night before on the layers of the earth. It was ironic because we were also studying density, and the density of each layer in the ‘rainbow’ was what kept them from blending into each other.

  6. How can we use it in normal routin?is it useable or not kindly reply

  7. I love the marble activity you did with him first to introduce

  8. Hey, I love this. Just started homeschooling my 10 yr old this year and he is very visual and needs cool things like this to help him learn in a fun way. Wish I was taught this way at school!!!!!!
    I was wondering is rubbing alcohol the same as acetone ( nail polish remover)?

  9. That’s a great idea, it amused me, I can only imagine how kids react and want to make this imagine immediately! Well, I want to try this myself, thought I’m already an adult. Thank you very much for sharing!

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