Rainbow milk

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Biology In Elementary Schools is a Saint Michael's College student project from a course that ran between 2007 and 2010 and fully described in this book chapter. The student-created resources have been preserved here for posterity. Link under 'toolbox' for printer-friendly versions of the exercises. Click on handouts to print full resolution versions. Please see Wikieducator's disclaimer, our safety statement, and the Creative Commons licensing in English and in legalese.

Rainbow Milk

Student worthiness

Tested and approved. It's a fun activity and a great learning experience!

Primary biological content area covered

Content covered:

This activity explores the sense of sight, nutritional needs, and the importance of milk and dairy in our diet.

In addition to the biological possibilities, educators can:

-Discuss color mixing.

-Discuss surface tension and what happens when it is broken. This can be related to plants and animals that live on the surface tension of bodies of water. Students can use their knowledge to figure out what happens to these plants and animals when pollutants break the tension.

  • Note: Although this is a simple activity, there are several concepts that can be addressed along with it. It can cover a variety of topics in any curriculum over an array of grades, depending on the depth of concepts covered... not to mention the fact that it's really cool!


  • Before you begin, make it clear to the students that they cannot drink the rainbow milk due to the dish liquid detergent used in the activity.
  • It is a good idea to supply students with eye goggles in case any detergent or food coloring splashes up from the bowl.


  • Food Coloring (red, blue, yellow)
  • Liquid Dish Detergent
  • 1 Gallon of Skim Milk (or enough to cover the groups of students doing the activity. Note: whole milk does not produce the desired result)
  • Bowls (enough for however many groups are going to perform the experiment)
  • Paper, or pre-made observation sheets
  • Markers, Crayons, or Colored Pencils
  • Bones (such as those from a model skeleton) can be used to demonstrate the importance of calcium.
  • Safety goggles (there is a chance some of the materials may splash up from the bowl).


  • Observation sheet (Here, students will record their hypotheses, and record observations before and after food coloring and liquid dish detergent is added to the milk.)

Description of activity

Students will actively mix three colors of food coloring with dish liquid detergent in a bowl of milk. They will hypothesize, and then observe the effects and record their findings. Students will also discuss the sense of sight, and the importance of milk and dairy to good health.

Lesson plan

1. Ask students to think about what colors are present in a rainbow. Have them share their answers by asking for volunteers.

2. Next, ask students how they know that these colors are in a rainbow. Most likely, at least one will say they know because they've seen them before. Use this opportunity to address the importance of the sense of sight, and to talk about what individuals do if their sight is impaired.

3. Now ask the students why milk is important for them. Show them The Food Guide Pyramid and talk about what it means. Discuss how milk and dairy contain calcium which helps promote the growth of strong bones and teeth. Now, explain that the activity they are about to complete will involve milk, and the colors of the rainbow (colors that they will be able to see because of their sense of sight).

4. *Perform the activity*

a. Give each small group of students a bowl containing milk.

b. Next have the students add several drops of blue food coloring, yellow food coloring, and red food coloring equally spaced around the bowl. The colors should be equal distances from each other, so each color should be placed about 1/3 of the way around the outer rim of the milk. Ask students to make predictions as to what will happen when the dish soap comes into contact with the food coloring; have them write their hypotheses down on their observation sheets.

c. Add a little bit of dish soap to the center of the milk.

d. Have students watch the colors carefully.

e. Once the mixture has settled (after about 5 minutes),have students make and record any observations regarding what has taken place to the milk and colors by drawing what they see on their observation sheets.

f. Next, have students blow softly into the bowls in order to swirl the colors together and create beautiful rainbow patterns.

5. Discuss the results and final comments with students.

7. Have students help clean up, and have them help pack up a box for the students who were unable to make the lab that day.

Potential pitfalls

The milk may not mix well with the elements provided. For example, the type of milk you use may not mix with the food coloring or dish liquid detergent to make a rainbow. Also, the colors may not move enough, and therefore fail to create the mixed-colored patterns. This dilemma can be fixed simply by blowing softly into the bowl after the dish detergent has been added to the milk and food coloring mixture. Some students may be over-zealous and shake the bowl, which will cause the milk to turn brown. It is important to monitor the students as they observe the color mixing so that they don't over-mix the dye. Finally, make sure that students do not touch the milk; doing so will cause movement which can make the food coloring move in ways that it shouldn't.

Math connections


Students can count the number of food coloring drops that they use for each color. They can then calculate the total number of drops of food coloring used in their experiment.

Literature connections

  • A Rainbow All Around Me by Sandra L. Pinkney
  • The Food Pyramid by Janine Scott
  • From the Rookie Read About Science series:

"All the Colors of the Rainbow" by Allan Fowler

Connections to educational standards

Predicting and Hypothesizing


Students demonstrate their understanding of predicting and hypothesizing by...

•Predicting a logical outcome to a situation, using prior knowledge, experience and/or evidence. Explaining reasons for that prediction.

Conducting Experiments-

S1-2:4 Students demonstrate their ability to conduct experiments by… •Referring to and following a simple plan for an investigation. AND •Describing observations using senses rather than feelings (e.g., The snail has a hard shell with wavy, brown lines, rather than the snail is awesome).

Next steps

  • This activity can be used as a hook to get students interested in rainbows. Following the activity, educators can begin discussing how real-life rainbows are formed.
  • The students can take this experiment a step further by thinking of other elements that they could mix with the milk, and then they could test the productivity of those elements by mixing them in with the milk and seeing if they have the same effects.
  • Students could also try the experiment in different grades of milk to explore if there are different reactions and why!

Citations and links

Definition of rainbow: http://www.enchantedlearning.com/Risfor.shtml)

Vermont State Standards:


Source of idea: http://www.kidzone.ws/science/rainbow.htm