Natural pigment chromatography

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Statement of Purpose

Students will explore natural pigment sources on campus and learn ways to harvest, process and use them, which will help them draw connections between the natural world, art, and concepts of stewardship.

Learning Goals: 

Enduring Understanding Emphasized:

  • Appreciate the natural world and cultural history of the area
  • Understand connections between art, science, and history

Knowledge developed:

  • Describe what pigments are, what they are used for, and some plants that can be used to acquire them

Skills developed:

  • Investigate pigments from local plants (from the forest or garden)
  • Connect this lesson to the rest of their experience at IslandWood (ethnobotany or garden E1T1, teambuilding, stewardship, ecosystem exploration, natural and cultural history)

Age group: 4th-6th

Venue/s: Garden, various sites on campus, art studio or lab

Materials: leaves, (could also be done with flowers, fruit, or vegetables); beakers or glasses; isopropyl (rubbing) alcohol; coffee filters; mortar and pestle

Time: xxxx

Set up: xxxx

Introduction:

Have you ever wondered why leaves change from green to an amazing array of yellow, orange and red during the fall? Leaves get their brilliant colors from color-creating molecules called pigments. Today we are going to go outside and gather natural pigments, then come in and process them, and use them. We are going to do science, art, and history in the lesson today.

Assessment:

(How will you know what your students learned from this experience, as a group and as individuals?)

  • Lead an initial discussion to assess what students know about natural pigments
  • “What do you think a pigment is?” (a pigment is a substance that gives color to something)
  • “Where do you think pigments come from?" (leaves, berries, rocks, soil, charcoal)
  • “What can pigments be used for?”


The core lesson:

•    Cut or tear the leaves into small pieces. Put each group of leaves into the bottom of a beaker or glass.
•    Add one tablespoon of rubbing alcohol to each glass.
•    Crush the leaves into the rubbing alcohol using a spoon or other utensil for about five minutes, until the solution is dark. 
•    Let the solution sit for 30 minutes in a dark place indoors.
•    Use a fork to remove any leaf pieces from the solutions and discard these, while leaving the liquid in the glass.
•    Pour each solution into a smaller container, and leave it in a dark place indoors to allow more of the alcohol to evaporate. You will be ready for the next step when you stir your solutions and they seem thicker.
•    Thoroughly stir each colored solution, using a different utensil for each solution so as not to mix the colors.

•    Prepare coffee filter strips. Cut up filters into long, one-inch-wide strips. They should be long enough to touch the bottom of the beakers or glasses and still extend over the top.
•    Using a toothpick or paintbrush for each color, smoothly and evenly "paint" some of each solution across a paper towel strip about one inch from one end. Because some plant pigments can stain, you should do this on a plate so that the color will not stain your work surface.
•    Allow the strips to dry.
•    While the strips are drying, pour enough rubbing alcohol into each glass jar to just cover the bottom. Prepare one jar for each student, or color solution.
•    Wrap the non-pigmented end of each strip around a pencil or twig, and carefully place the twig over the opening of your vessel until the end of the strip just touches the alcohol. Make sure that each strip is not touching the jar's sides. Place and secure strips from the same solution into the same jar, but keep them from touching each other.
•    Let the glasses sit for 30 minutes and watch the paper strips. 
•    When one of the colors reaches the top of a strip, remove strip and let dry.
•    Look at the different dried strips, and notice the order in which the colors appear on the different strips. 

Discussion Questions to enhance learning:

Throughout the lesson:

  • How does the color of the alcohol change when mixed with the crushed plant material?
  • What happens to the color of the paper strips?
  • How are the colors in the strips different?
  • Do strips from different color solutions have unique colors, shared colors, or both?
  • Is the same color on the same place in different strips or is it in a different place? Do the colors appear in the same order or in different orders on each strip?

Conclusion:

(reflection and transfer of knowledge this is essential! How can you ensure that your students are able to transfer new skills, knowledge or understanding beyond the activity: other parts of the IslandWood experience, home, school?)

  • What kinds of colors did we find in the field today? Were you surprised?
  • At what points in this lesson did you feel like a scientist? When did you feel like an artist?
  • What colors did we NOT find? Why do you think that is? What sources do you think we could use to get those colors?
  • Has this changed the way you look at your natural surroundings?
  • How do these pigments fit into the ecosystems you’ve been studying and exploring at IslandWood?
  • How did teamwork fit into the activity today?
  • What kinds of pigments do you think you could find in your home neighborhood, or at school?
  • What else could we do with these pigments?

Safety Considerations:

  • Stewardship – safe harvesting techniques
  • If harvesting fruits or vegetables – knife safety
  • Rubbing alcohol – depending on where your students are at, you could measure the rubbing alcohol out for them, or have them measure for themselves
  • Although there is an element of creativity in creating these pigment profiles, emphasize that it’s not about whose result was ‘best’, but the process of exploring the natural pigments

Background information:

There are many types of pigments in plant leaves. Chlorophyll makes them green and helps carry out photosynthesis during warm, sunny months. As fall arrives and the green, food-making color fades, other pigments such as yellow, orange and red ones become more visible.

Xanthophylls are yellow pigments, and carotenoids give leaves an orange color. Photosynthesis also uses these pigments during the summer, but chlorophyll, a stronger pigment, overpowers them. These pigments take more time to break down than chlorophyll does, so you see them become visible in fall leaves. They're also found in carrots, daffodils, bananas and other plants that have these vibrant colors. There are also anthocyanins, intense red pigments that aren't made during the summer, only appearing with the final group of the fall colors. These molecules also give the red hue to apples, cranberries, strawberries and more.

Although a leaf is a mixture of these pigments, you can separate the colors using a method called paper chromatography. This process dissolves the pigments and allows them to be absorbed by a strip of paper. Larger molecules have a harder time moving in the woven paper and get trapped in the paper first, whereas smaller ones travel farther along the paper. This process separates the mixture of pigments by molecular size—and by color.

While it may seem like there is a lot of background information necessary to complete this lesson, it is important to realize that this can be modeled as an investigation and exploration, where the outcome is not as important as the process. Stress to students that natural pigments are volatile and results will vary. Even if you are not the most knowledgeable about this process, it can still be a really valuable experience for students (and you!). Remember to be flexible, be curious, and have fun!

References:

This should include any books, articles, or personal resources you used in developing this lesson. Include sources of a lesson you may be adapting…


Created/Adapted by Margaret Cummings on 11/5/15 .