Yesterday on Twin Cities Live, I demonstrated some fun botanical science projects for learners of all ages, including Vegetable Vampires and Leaf Chromatography.
This fun art/science project lets you transfer plant pigments to cloth, creating beautiful prints of your favorite leaves and flowers. It’s especially great for fall, when there are so many colorful leaves around.
-Fresh leaves and flowers (Dry leaves won’t work.)
-A hard, smooth pounding surface, like a wooden cutting board or carving board
-Wax paper or plastic wrap
-Mallets or hammers
-Untextured cotton cloth, like a dishtowel. Heavy cloth works better than very thin cloth.
-*Alum and baking soda to treat cloth (This is optional. I don’t pre-treat my fabric, but the treatment step will help bond and preserve color, if you want to frame your prints. You can also buy fabric that’s pre-treated for dyeing.)
Safety tips: Protective eye wear is recommended. Young children should be supervised when using mallets and hammers.
What to do:
*If treating cloth: The day before you do the project, add 2 quarts water to a large pot. Add 1 Tb alum and 1 tsp baking soda to the water. Add the cotton and bring to a boil. Simmer for 2 hours, turn off heat and soak for at least two hours. Let fabric dry.
The next steps are the same, whether you’re using an untreated piece of cotton or treated cloth.
- Take a walk to collect colorful leaves and flowers. Choose plants that can be flattened. Flowers with huge centers, like coneflowers don’t work as well, but petals may be removed and pounded.
- Cover the pounding surface with waxed paper or plastic wrap.
- Cut a piece of cloth that will fit on the pounding surface when folded in half. Iron the fold.
- Open the cloth and lay it on the pounding surface. (See image above)
- Arrange leaves and flowers on the cloth.
- Fold the cloth over the plants and pound it with the hammer or mallet. If you’re using a hammer, pound more gently.
- Pound until you can see the forms of the leaves through the fabric. As the pigment leaks through, you’ll see the outlines of what you’re smashing. Hint: Hammers work better than mallets for fall leaves. For juicy leaves and flowers, use a mallet or hammer gently.
- When you’re finished pounding, unfold the fabric to reveal the print you created. Remove the leaves and petals.
- Label the image with plant names, enhance it with paint or markers, or leave nature’s design to speak for itself.
The Science Behind the Fun:
Pigments are compounds that give things color, and many of them are found in nature. Flowers, leave, fruits and vegetables are full of brilliant pigments. In this experiment, we transfer plant pigments to cloth by bursting plant cells using pressure from a hammer or mallet.
The green pigment found in leaves is called chlorophyll. In the fall, many trees stop making chlorophyll, and the red, yellow and orange pigments inside the leaves become visible.
Although you create a mirror image of leaves and flowers, you’ll notice that the color may be more intense on one side of the print. A waxy covering called a cuticle covers leaves, and is sometimes thicker on the top than on the underside of the leaf. It may affect the transfer of pigment to the cloth, making it easy to see structures like veins on the leaf print.
What parts of the leaf can you identify in the print you created?
This morning, on Kare11 Sunrise, I showed off my new book, Kitchen Science Lab for Kids, and demonstrated three experiments from the book. Just click on the experiment name for directions, photos and more about the science!
Frankenworms– Bring gummy worms to “life” using a chemical reaction.
Magic Bags– Explore the elastic properties of polymers.
Leaf Chromatography– Separate plant pigments on coffee filters.
This is especially fun in the fall, when you can compare green leaves to red and yellow ones! Here’s a nice article on the chemistry of the colors of fall leaves (from the Compound Interest website) that my friend Joanne Manaster highlighted on her Joanne Loves Science Facebook page.
What started out as a food science experiment turned into a seasonal one this morning, and we ended up outside pulling leaves off our Maple tree to see how the pigments from a red leaf would compare to those from a green one. Liquid chromatography allows you to separate the pigments (molecules that give plants color) using paper as a solid medium for the molecules to travel up, and alcohol as the solvent that separates and carries the pigments up the paper at different speeds, depending on how large they are.
To do this experiment, you’ll need a green leaf, and one or more that has turned color (we found a red and green one from the same tree!) In addition, you’ll need a coin, a jar, a pencil, paper towels or coffee filters and rubbing alcohol. Young children MUST be supervised during this experiment since rubbing alcohol is a toxic substance if ingested!
Balance the pencil on the lip of the jar and cut a strip of paper towel or coffee filter long enough to hang (folded in half) over your pencil and dangle with both ends just above the bottom.
Draw a pencil line about half an inch above the bottom of the strip on one side. Wrap a leaf around the coin (dimes work well) and press it down against the line on the left side, hard enough to rub color onto the line. (See photo above!) Do the same thing with the other leaf. Get as much color as possible onto each spot and let dry for a few minutes, or dry with a blow dryer.
Fill the jar with just enough rubbing alcohol so that the bottom of the strip will touch it, but the spots of color will not. Hang your paper strip over the pencil with the bottom touching the alcohol. (You can have it doubled or have one half hanging outside the jar. Both worked for us.) Try to make sure that the strip is hanging evenly so the color will travel straight up.
Watch as the colors travel up the strip and take the strip out of the alcohol before they reach the top. Let it dry and observe. The colors may be faint, but you should be able to make them out.
What do you see? Green leaves contain a pigment called chlorophyll, which helps plants do photosynthesis (get energy from sunlight, water and carbon dioxide.) In the fall, many trees stop making this pigment, which is why the other colors in the leaves become visible. Are your results consistent with this?
We tried the same experiment to compare spinach leaves that were fresh or had been microwaved in a ziplock (blanched). Although I read that the pigments change when vegetables are cooked or stored, we didn’t see much difference, except a brown smear near the very bottom. What other veggies could you try this experiment with?