Color Control

1. Cut a 2-inch square from a coffee filter or a paper towel. Using a Sharpie marker, draw the lines shown in the diagram on the PDF. Make sure to draw the boundaries dark enough to avoid color leaking issues.


2. Cut away the shaded area to leave two tabs (A and B) on the bottom.


3. Pour water into the cups, filling them close to the top. Add one color of food coloring to each cup, enough to make the colored water very dark (10 drops or more). If you want to try different color combinations, you are definitely welcome to do so! Swirl gently to mix.


4. Place the coffee filter into the cups so that tab A dips into one color and tab B dips into the other. You can hold the paper device simply by hand or using a clamp (clothes pin) or tall glass to support it.


5. Watch as the colored water moves up the filter. What happens as the path divides? Try drawing other designs and see how the flow can color them!

Clean-up:

Colored water can be poured down the drain. Throw coffee filters in the trash. Please be aware that the sharpie leaves stain on the desk, which can be cleaned up by isopropanol or alcohol.

You may have noticed that the colored water stayed inside the lines as it moved up the strip. Different materials have different chemical properties that affect how they behave with water. Hydrophilic materials attract water, making contact and mixing easily. Hydrophobic materials repel water, beading up or separating out. In this case, the ink in the Sharpie marker is hydrophobic and repels water, so the colored water cannot cross the lines you drew. This allows you to control how the water flows and where the colors mix. Also, since paper has a porous structure, the colored water can freely flow through the pores.

This behavior is important for materials scientists because they can use the hydrophobic/hydrophilic boundary to direct fluid flow and design different mixing effects. Also, since paper is widely available and easy to use, it is an ideal material to use for building inexpensive devices. For example, chemicals can be added to the paper that can react with a certain solution when it comes into contact. This can be used for building devices such as pregnancy tests or blood glucose measuring kits. Currently, new paper-based materials are being developed to perform many kinds of medical testing which can be used at low cost in parts of the developing world or for detecting harmful environmental toxins like lead and other heavy metals

Sometimes, going simpler is better. Experimenting with paper, liquid, and other basic materials, Frank Gomez and Alexis Basa are designing new sensors that could help save people’s lives around the world.

Below are suggested alignment between this activity and concepts in the Next Generation Science Standards.

Performance Expectations

• 2-PS1-2: Analyze data obtained from testing different materials to determine which materials have the properties that are best suited for an intended purpose.


• 5-PS1-3: Make observations and measurements to identify materials based on their properties.


• MS-PS1-2: Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred.

Disciplinary Core Ideas:

PS1.A: Structure and Properties of Matter

2nd Grade

• Different properties are suited to different purposes.

5th Grade

• Measurements of a variety of properties can be used to identify materials.

Middle School

• Each pure substance has characteristic physical and chemical properties (for any bulk quantity under given conditions) that can be used to identify it

Please click on the PDF below for a more detailed description of how this activity ties to NGSS