A prior ChemShorts for Kids article looked at how soap interacts with water molecules. You can see another application of the behavior of soap in water in this activity, where food coloring is added to shaving cream and the resulting colors are transferred onto paper. The result is a very cool marbling effect―you can make marbled paper!
Materials
• Craft stick, ruler or flat piece of cardboard (to remove lather from the paper)
• Food coloring
• Paper (card stock works best)
• Paper plate or baking tray (it should be larger than the paper)
• Shaving cream with lather (no gel)
• Toothpick
Be Safe!
Food coloring will stain skin and clothes. For best results, work with an adult to supervise or guide you.
Experiment
Spray shaving cream onto the paper plate or tray and spread out the lather so it covers a space larger than the paper. The lather should be at least 1–2 cm high. Sprinkle the surface of the lather with different colors of food coloring. Drag a toothpick through the food coloring until you get a nicely marbled pattern. Place the paper on the colorful lather, making sure that it completely covers the surface of the paper. Peel the paper away from the lather and use a craft stick or ruler to scrape off excess foam. Allow the paper to air dry. If the colors remain bright you can usually repeat the process with another piece of paper.
Food coloring marbled into shaving cream.
What’s happening?
Shaving cream is a foam made up of air bubbles trapped in liquid soap. Soap molecules have both polar and nonpolar groups and are thus attracted to water (through the polar ends) as well as oils (nonpolar). The molecules in food coloring are polar and are easily dispersed throughout the foam.
Likewise, paper is also a very polar material made up of cellulose fibers with thousands of glucose molecules joined together in long, zig-zag-like chains or threads.
Cellulose fibers with glucose molecules joined together in chains—oxygen atoms are shown in red
Jutting off the top and bottom of these “threads” are many highly polar OH groups that are part of the glucose molecule units. These groups attract the dye molecules in the food coloring so that the marbled colors stick to the paper even after it is removed from the lather.
Explore more at
https://happyhooligans.ca/marbled-paper-shaving-cream-food-colouring/
http://www.exo.net/~jyu/activities/shaving%20sumi.pdf
To view a treasure trove of past “ChemShorts for Kids” activities, go to:
https://chicagoacs.org/ChemShorts
