In this blog we are returning to some of the early columns of Ask Your Science Teacher,  published in 2009. The columns are updated and revised. Many originally ran in The Tomah Journal at the behest of John Kenny, Publisher. We hope you enjoy them, and please give feedback.


In our science class, we learned that black is not a color, so how do we get black ink or black paper?


            Most things we see in everyday life do not give off light. Their color depends on the light waves they absorb or reflect. For example, grass is green because the chemical chlorophyll reflects principally green light. Grass absorbs the other colors such as blue, red, and yellow. Indigo is a dye put in blue jeans that reflects blue, but absorbs red, green, and yellow.

            Objects that are black absorb most all the colors of the sun’s spectrum or what we call the seven colors of the rainbow. If a number of chemicals are mixed that will absorb nearly all colors, that object will appear black.

            Try this experiment to separate the chemicals used in black ink. You need a cup of water, two coffee filters, and a water-soluble black felt tip pen. Cut a hole in the middle of a coffee filter. Put some ink spots around the hole. Make a cone-shaped wick from another coffee filter and insert it through the hole. Set the coffee filter on top of the water-filled cup with the cone shaped filter sticking into the water and acting as a wick. Observe the water advancing up the wick and spreading across the ink spots. Lift the coffee filter off the cup and set it across an empty cup to let it dry. How many different colors do you observe? The experiment you performed is called chromatography.

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