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

Grab our Super Cool Science Kit including 22 more experiments and awesome follow up observation sheets for young scientists.

Super Cool Science Kit - 2000

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.

Latest posts by Jen Rice (see all)


  1. 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?

  2. This would be fun for Grayson

  3. 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

  4. 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.

  5. Such a cool experiment! I am adding this to our Summer Fun Pinterest Board!

    I would love for you to share this post {and others} at my Show Me Saturday linky party. We are live now!

  6. sounds great for my little pre-schoolers says:

    i hope 3-4 year old children can do this/ with an adults help.

  7. Elisabeth Kennard says:

    Learning all sorts of things – listening to instructions, patience etc as well as Science – & having fun – great

  8. After a day will everything mix in the jar

  9. Dee Dee says:

    I just made this with my 7 & 9 year olds for a summer activity. We even looked up the molecular density of each of our ingredients and predicted what might happen. They look great and the kids enjoyed doing them!! Thanks for such great idea!!

  10. our flopped just a black blob….lots of wasted ingredients!


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