MnSTEP Teaching Activity Collection > MnSTEP Activities > Rainbow Milk

Rainbow Milk

Lisa Schoneman
Halverson Elementary
Albert Lea, MN


In this classroom experiment, students will experiment with how fat and soap molecules repel each other and how colors mix to make new colors.

Learning Goals

This activity is designed for students to learn how dish soap works in water. It also shows them when two primary colors mix together, it will make a new color (secondary color).
Vocabulary words: primary colors, secondary colors
Key Concept: primary colors mix together to make secondary colors.

Context for Use

This activity is best used in kindergarten during a colors unit. The activity itself should be completed with small groups of students (3-5). This activity will take about 5 minutes with each group. To complete the lesson the following materials are needed: coated paper plate, whole milk, food coloring, dish soap (Dawn works the best), q-tips. Students will be introduced to the concept of color mixing.

You could easily make this into a science lesson for older students. You could have them experiment with different fat contents in milk (skim, 1%, 2%) and different types of dish soap.

Subject: Physics:Optics
Resource Type: Activities:Classroom Activity
Grade Level: Primary (K-2)

Description and Teaching Materials

This activity will be used in conjunction with the colors unit in Kindergarten. It will be introduced talking about colors and how colors can make new colors when mixed together. There are many stories that can be used, such as Mouse Paint by Ellen Stoll Walsh, Color Dance by Ann Jonas, or your favorite color story.

Materials needed:
Whole Milk
Dinner plate or coated plastic plate
Food coloring (red, yellow, green, blue)
Dish-washing soap (Dawn brand works well)
Cotton swabs (q-tips)

1. Pour enough milk in the dinner plate to completely cover the bottom and allow it to settle.

2. Add one drop of each of the four colors of food coloring - red, yellow, blue, and green - to the milk. Keep the drops close together in the center of the plate of milk.

3. Find a clean cotton swab (q-tip) for the next part of the experiment. Predict what will happen when you touch the tip of the cotton swab to the center of the milk. It's important not to stir the mix just touch it with the tip of the cotton swab.

4. Place a drop of liquid dish soap (the Dawn brand works well) on the tip of the cotton swab. Place the soapy end of the cotton swab back in the middle of the milk and hold it there for 10 to 15 seconds. Look at that burst of color!

5. Add another drop of soap to the tip to the cotton swab and try it again. Experiment with placing the cotton swab at different places in the milk. Notice that the colors in the milk continue to move even when the cotton swab is removed. What makes the food coloring in the milk move?
Since this is the introduction to the unit I will have the students use colors to indicate what colors mix together and the new color that was created. This will tie into the lesson for the next day on color mixing using pipettes and well trays.

Teaching Notes and Tips

This activity is best done in a small group as it is hard for an entire class to see at once. It can be done but the students will not get a close up look as to what happens. It is best if you have a plastic plate or a coated paper plate as milk will seep through a non-coated plate. It is also best if you can try to not bump the table once you have started. It will start the mixing of the colors before you want it to.


Most of the assessment will happen with observation. I will also be observing the students use their markers to create the new colors they saw.

Standards Scientific inquiry is a set of interrelated processes used to pose questions about the natural world and investigate phenomena.

References and Resources

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