With this easy St. Patrick’s Day rainbow science experiment, you’ll infuse color and excitement into your school day! Read the experiment instructions below, followed by discussion questions, scientific and historical background, and connections to Scripture to create a meaningful science study in your home.
Using the principle of capillary action, you can watch water jump from one glass to another all while creating the colors of the rainbow.
Here are the simple steps:
First, gather paper towels, red, blue, and yellow food coloring, and six glasses (mason jars work well).
Next, add a cup a half of water to three of the jars. Leave an empty jar in between each of the water jars. Add about 20 drops of food coloring to each of the water jars. Red in one jar, yellow in a second, and blue in the third jar.
Now, fold a half sheet of a paper towel long ways twice, so that it now looks like a long bookmark. Place one end of the paper towel in a jar with water and bend the other end into the adjacent empty jar so that it nearly touches the bottom of the jar. Repeat this process until all jars have one paper towel going into the jar and one paper towel going out of the jar.
After just a few seconds, you will see the water creeping up the paper towels. After a few hours, you will see the water beginning to flow into the empty jars and the primary colors mixing to create the secondary rainbow colors. If you leave the jars overnight, you will find that all six jars have the same amount of water in them by the next day!
Before you begin this activity, ask your students to explain gravity. What direction do objects normally move? Could we ever get a liquid to move upward instead of downward? How? Can they think of any instances in nature when water moves upward?
Now show your students the materials you will be using and ask them how we can get water from the full jars into the empty jars without pouring it. What are the paper towels for?
You can choose to explain the science behind this experiment at any point, but it may be fun to let them watch the water moving up the paper towel first, before you read the explanation.
So how does water move up the paper towel in what seems to be an action that defies gravity? This phenomenon is called capillary action, and it is the same action we see in plants as water moves up their roots through their stems into their leaves and petals.
Because water molecules like to stick together (called cohesion), this creates surface tension, which allows water to form little beads instead spreading out. It also allows water to get sucked into little spaces or gaps in materials. Adhesion helps this process by attracting different molecules to one another.
In the case of our paper towels, the fibers are made of cellulose, which has a slightly positive charge on one end and a slightly negative charge on the other end. Water molecules are designed in this same manner. This results in the water molecules attaching to the cellulose and “walking up” the paper towel and creating a rainbow.
What does this have to do with St. Patrick?
St. Patrick was born in the 5th century Britain but sold into slavery in Ireland when he was 16 years old. He escaped back to Britain, only to later return to serve as a missionary to the pagan Irish. He is largely credited for bringing Christianity to Ireland and was already a legendary figure by the 7th century.
The Scriptural account of the worldwide flood in Genesis 9 concludes with God’s promise in the form of a rainbow never to destroy the earth through a flood again. Read that account together. What does God say about rainbows?
It is thought that this Scriptural account merged with Irish myths and traditions to become a symbolic part of the St. Patrick’s Day holiday.
What made you say Wow?
We like to wrap up all of our Science with Friends projects with this fun question as a way to help students reflect on what they have observed and create a lasting memory sticking point. It is also so fun to hear what parts amazed them the most!
Want more science?
Each of our Science with Friends bundles includes a Parent Guide with discussion questions, scientific background, and connections to Scripture. We believe science study should be filled with wonder, curiosity, and meaningful conversation – not simply kitchen tricks that are forgotten the moment they are over.