If you were painting and ran out of black paint, what would you do? You might try to mix many of the colors you have together to create a dark pigment to use. Black ink is typically made out of several colors combined. Not all black pigments are the same! Some have a brown hue, while some have more of a blue or purple tinge. It all depends on the pigments used to create the black color.
When inks that are water-soluble mix with water, they can separate out into the different pigments used to create them. You can see this happen using a process called chromatography.
How to do the Separating Inks STEM Challenge
The Challenge: Separate black ink into various colors.
Materials: coffee filter paper, a variety of black markers or pens, long skewers (or straws), a small tub filled with 2 cm of water
Challenge Criteria: Cut the filter paper into long strips that are the same size. You need one strip for each marker/pen you chose to test. Draw a thick black horizontal line 4 cm up from the bottom of each strip with the different markers/pens you chose. Tape the other end of each strip to the skewer. Lay the skewer ends over the top of the tub with water so the ends of the filter papers touch the water, but the black lines should be above the water level. Depending on the size of your tub, you may need to adjust the amount of water. Wait about 5 minutes, watching the water travel up the filter paper.
Reflection
What are some different colors that came out of the black inks? Were there any inks that did not separate at all? If so, why do you think this is? Which inks had the most interesting pattern appear?
Challenge Extension
Repeat the experiment with inks of different colors.
