What are you learning? How a color separates into its various pigments.

The Experiment
1. Spread open the coffee filter on a protected table and place the quarter in the filter's center. With the marker, draw a circle on the filter by tracing around the quarter.
2. Fill the paper cup with water.
3. Set the plastic cup open side up on the table and stretch the filter over the mouth of the cup.
4. Dip your finger in the water, then touch the center of the circle with your wet fingertip. Watch the wet spot on the filter until the ink stops spreading.
5. If there are any dry areas inside the circle drawn on the filter, repeat step 4.

The Aha! Effect When ink comes into contact with water, it begins to separate into different colors. Depending on the ink used, varying amounts of blue and yellow can be seen (the filter will look like a tie-dyed T-shirt).

Why Does This Happen? Ink is a mixture of a fast-drying liquid and pigments--substances that give material color. The pigment of the dried ink on the filter dissolves in the water. Then this watery mixture is absorbed by and moves through the filter paper. The different pigments have different amounts of attraction to the filter paper; the color with the least attraction moves a greater distance through the paper. Generally, says VanCleave, blue pigment in ink moves farthest, followed by yellow. The method of separating the parts of a pigment mixture like this is called chromatography.

Go One Step Further Follow the previous steps, but this time, use a black water-soluble marker to draw a circle on the filter paper. Black ink usually will separate into three colors: red, blue, and yellow.

Adapted from JANICE VANCLEAVE'S HELP! MY SCIENCE PROJECT IS DUE TOMORROW! (John Wiley & Sons, 2001).