Science for Kids: Rainbow Jar

Science for kids ages 2 and up.

We love fun science for kids and this easy activity is one of our favorites. With just a few household ingredients, you can actually pour a rainbow in a jar. Cool, huh?!

Science for kids, kids science, rainbow jar, make a rainbow in a jar

Rainbow Jar Supplies

This project requires quite a few things but most of it is probably stuff you already have lying around your house.  To get ready for the science activity, I grabbed my supplies.

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

  • 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, C, 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 a little kids’ science. I introduced density by explaining 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!!  First we poured in the honey.  Be sure to pour it into the middle of your container — don’t let it touch the sides.

Next he poured in the corn syrup. {We’d colored it purple using the food coloring.} Again,  pour it into the middle of the container, not touching the sides.

Then we added the dish soap.

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 next. Do you know what I’m going to say? That’s right, pour 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.

Rainbow Jar 3

BUT WAIT! DON’T POUR IT IN THE MIDDLE!   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. Fun kids' science experiment. Make a rainbow in a jar. {Playdough to Plato}

Find More Science for Kids

For more fun science for kids, make gummy worms dance, try out some STEM activities, and walk on eggs.


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About Jen Rice

Jen is a mom of two {ages 5 and 1} who loves cross stitching, surfing Pinterest and finding fun and creative ways to get her kids learning.


  1. Jackie Embry says:

    Can’t wait to try it.

  2. So fun! I did this with a group of 3rd graders today, and they thought it was amazing! Thanx for the great idea!!

  3. Jonetta Mason says:

    Going to do this tomorrow with my three year olds.

  4. Thank you for a great idea! I’m looking forward to do this with the children in the preschool where I work. I live in Sweden and corn syrup isn’t something we have here. Is there anything I can replace it with, or is it an option to just skip it? Is it like any other syrup?
    Thank you for your answer!

  5. I am happy to read that the rainbow jar is helpful, Jenny!

    You could skip the corn syrup. You will lose a layer but it will not be too noticeable.

    Fingers crossed that your preschoolers love the activity too!

  6. Has anyone shook up the bottle? what happened? did the layers separate again? I know that my pre-kg kids will shake up the bottle, so I just want to be prepared!

  7. Divya K says:

    Lovely! As a chemistry teacher though I cringed a bit at the explanation. I know you’re trying to simplify for kids, but it will make it more confusing when they’re older. Instead of more marbles, put the same number of, say, marbles and packing peanuts in two cups. They take up about the same amount of space, and have around the same number of pieces (molecules) but one is heavier than the other because there are either more small particles or heavier small particles (atoms for your reference) in each bit of space. Or you can compare balled up paper to stacked paper. Put as much of each as you can in a shoebox (same volume) and the stacked paper box will be heavier. More ‘stuff’ (matter) can fit into the same space so that shoebox (unit of volume) is heavier.

    There are NOT necessarily more molecules in denser liquids in the same amount of space… There could be more, there could be fewer. There IS more matter in that bit of space than for the less dense liquid. (I keep emphasising ‘same bit of space’ because you can’t compare the weight of one cup of water to one drop of oil- density is mass per unit volume. It’s like that brainteaser, what weighs more, a ton of feathers or a ton of bricks? They both weigh the same! But the bricks will take up much less space because they’re more dense. Or to flip it, if you have identical boxes filled with bricks vs feathers the box of feathers will be lighter because they’re less dense. See why volume is important?)

    I know this may sound pedantic, but it really does make a difference later. And my students always complain that every year they need to unlearn the ‘lies’ they were taught before (their words not mine!)

    Thanks for hearing me out!

  8. Very interesting activity for kids. I’ll try it very soon with my pre school kids. Thanks for sharing it to us.

  9. So excited that you’ll be making a Rainbow Jar with your preschoolers, Raouza!! Let us know how it goes. :)

  10. Thanks much for this pretty, graspable activity. And thanks to DIVYA K for your insights.

  11. hi there. You say not to let some ingredients like honey or the syrup touch the sides. So does it have to be a very thin layer for those ingredients? Because i immagine that as one pours them in the middle they will inevitably start “sliding”/”slipping” towards the sides…

  12. Darling little boy! :)
    Thanks for sharing rainbows!

  13. I’m with Kristi. What happens if the liquids mix? after a while like when the kids come back the next day will it be a rainbow again or will the food coloring mix together but the liquids separate?

  14. This would be fun for Grayson

  15. i think what she is saying by ” don’t touch the sides is don’t pour your liquids down the side of the jar, like if you were pouring a pop/soda into a glass and you pour it on the side of your glass to avoid fizz and making it flat. It will spread to the sides as you pour the layers

  16. well the first thing my little one wanted to do was shake this thing up and we got done with it so we will see if it will separate doesn’t look like it’s going to but we will see and by the way I use the brick density thing for my daughter cuz I kinda thought the marble thing was a little wrong to.


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