Key concepts
Chemistry
Solutions
Miscibility
Polarity
Surfactants
Surface tension
Introduction
Are you in need of cards for family or friends? No problem—in this activity you will create beautiful artwork and practice science at the same time! The only materials you need are shaving cream, food coloring and sheets of paper. Ready to discover where the science is hiding? Go ahead and find out!
Background
Paper marbling is an artistic method in which colors floating on a liquid surface are transferred onto paper to create a marbled pattern. The art of paper marbling dates back to the 10th century where Japanese artists developed a technique called suminagashi, which means “floating ink.” Oil-based ink is dropped into a shallow pan of water where it floats on the surface. Paper is laid on top of the floating ink, and the color transfers to the paper’s surface.
Another paper-marbling method that originated in Turkey and central Asia involves a thick liquid, called size, made from substances such as cornstarch. In this method the liquid has to be thickened because the colors used are water-based and would otherwise not float. To make the colors float and spread even better they are mixed with surfactants then dropped onto the size, which results in a pattern of floating color that can similarly be transferred onto paper.
This ancient art technique actually involves a lot of science! The colors float because they are less dense than water. It is also important that the colors and the water do not mix. Whether a liquid mixes with another depends on their individual molecular structures. The molecules that make up a liquid can be either polar or nonpolar. The simple rule “like dissolves like” says polar substances dissolve in polar liquids and nonpolar substances dissolve in nonpolar liquids. Water is polar whereas oil is nonpolar, which is why they don’t mix.
Substances that dissolve in water are called hydrophilic; those that do not are hydrophobic. Surfactants are added to the colors to influence their spreading behavior. These special molecules can do this because they have two ends: one hydrophilic, the other hydrophobic. This property of surfactants allows substances to spread out better because it decreases water’s surface tension, which results from water molecules holding together at the surface because they are slightly attracted to one another—more than they are to the air above.
In this activity you will do a simpler version of paper marbling using shaving cream and food coloring. It sounds different but the same concepts apply. See for yourself and do this fun artistic science activity!
Materials
- Two large plates
- Shaving cream (not gel)
- Liquid food coloring (at least two different colors)
- White paper or card stock
- Medical dropper
- Scissors
- Spoon
- Toothpick
- Jumbo craft stick
- Paper towels
- Spray bottle
- Water
- Workplace that can tolerate spills
- Adult helper (optional)
- Iron (optional)
- Vegetable oil (optional)
- Rubbing alcohol (optional)
Preparation
- Place the two plates next to each other on your workspace.
- Cut two letter-size pieces of paper in half crosswise. Then fold each in half, creating two folded cards.
- Put water in the spray bottle, and set it aside.
Procedure
- Put shaving cream on the two plates, and spread it out with your hands or a spoon to create a layer with an area at least as large as your paper card and a depth of about half an inch. How does the shaving cream feel? More like a liquid or a solid?
- Take the first color of your food coloring and add several drops on top of the shaving cream using a medical dropper or dripping it straight from the bottle. Do this with both plates. What happens to the color once it drops on top of the shaving cream? Does it mix with the foam, sink into it or stay on top?
- Repeat with all other food colors you want to use. Do all the colors behave the same way? Can you see a color pattern develop on the foam's surface?
- Next take the toothpick and carefully swirl around the color in the shaving cream until you have created a color pattern that you like. Try not to overmix the colors. What happens when you swirl the colors around? Do they mix with the shaving cream or do they stay separate?
- Use the spray bottle to spray some water on top of the color pattern on one of the plates. Use at least five to 10 pumps of water. Then let the foam sit for about one minute. Does the color pattern look different once you have sprayed the water on top? How does it differ from the color pattern on the other plate?
- Place your first card with the front side facing down on top of the shaving cream and press it lightly so that the whole card is covered by the shaving cream.
- Repeat with the second card and the second plate.
- Carefully remove both cards from the shaving cream, turn them around and scrape the remaining cream from the cards’ surfaces with the craft stick. What do you see on the paper once the shaving cream is removed? Do you notice a difference between the two cards? Can you explain your results?
- Let the cards dry. If the paper wrinkles, you can ask an adult to carefully iron it at the lowest heat setting and another sheet of paper between your card and the iron.
- Extra: Try to play around with more colors, different swirl patterns and varying sizes of paper. How many different patterns can you create?
- Extra: What happens if you spray oil or rubbing alcohol instead of water on top of your color pattern? Will your results differ? Get some vegetable oil and rubbing alcohol to find out!
Observations and results
Were you able to make beautiful marbled paper cards? The shaving cream–marbling method works very similarly to the others described in the beginning. Shaving cream is made of a mixture of soap and water with a gas that can turn liquid into foam when you spray it out of the bottle. Soap is a surfactant, which means its molecule has a hydrophilic (water-loving) and hydrophobic (water-repelling) end. Liquid food coloring is a mixture of dye in water or alcohol and is hydrophilic. When you drop the food coloring on the shaving cream, it won’t soak in because it can only interact with the hydrophilic parts of the soap molecules and is repelled by the hydrophobic ends. Even if you swirl the colors with a toothpick, you still see a distinct separation between the color and the shaving cream.
When you put the paper on top of the color pattern, the food dye gets soaked into the paper, transferring the whole pattern onto its surface. This is because paper is made from wood pulp, which mainly consists of cellulose found in the cell walls of green plants—a hydrophilic molecule. The hydrophilic food dye can spread easily across the paper, creating a beautiful marbled pattern. When you spray water on top of your pattern before you put the paper on top, however, the food dye mixes with the water and is carried into the deeper layers of the foam. You might have noticed your color pattern looked washed out after adding the water. The pattern on the paper does look much fainter than the other one—but it is just as beautiful!
Cleanup
Use paper towels to remove the shaving cream from the plates, then dispose of everything in the trash. After you rinse the plates with hot water and soap you can reuse them. Don’t throw away your cards—you might want to send them to family and friends!
More to explore
Surfactant Science: Make a Milk Rainbow, from Scientific American
Surface Tension, from HyperPhysics
Explained: Hydrophobic and Hydrophilic, from MIT News
Science Activities for All Ages!, from Science Buddies
This activity brought to you in partnership with Science Buddies
