lesson 2: investigating iridescence

1Investigating Iridescence

Lesson 2: Investigating

Recommended for:

Learning Objective:

Estimated Time:

Key Vocabulary: pigmentiridescencenacre

30 minutes

Students will investigate iridescence and create their own iridescent paper craft.

There are two primary ways animals produce color: through pigmentation or through structure (or a combination of the two). Pigments are colors that an animal makes, such as melanin that gives us humans our skin color, or colors they ingest, such as carotenoids from seeds and berries that give northern cardinals their bright red feathers. Structural color comes from the microscopic shape of an animal’s tissues. The color is produced depending on how the light hits the structure, causing the wavelengths to be diffracted or reflected. For instance, morpho butterflies have specially shaped scales on their wings that cause them to appear blue at certain angles.

The iridescence on the inside of an abalone shell is an example of this structural color. The iridescent coating, also called mother-of-pearl or nacre, is secreted by the abalone’s mantle. To build their shell, abalone combine minerals acquired from the surrounding water (e.g. calcium) with organic proteins in the body. The resulting shell is incredibly strong, protecting the abalone from predators and wave action. The iridescent coloration in the shell’s interior is a by-product of its structure, caused by the diffraction of light hitting the surface.

Animals may be iridescent for avariety of reasons; for example, morpho butterflies may be blue to attract mates and to evade predators. So why would an abalone have iridescence on the inside of its shell where it can’t be seen? It turns out many species of snail have nacre on the innersurface of their shells. The most commonly accepted reason is that the shimmering color is incidental – nacre is a strong material and primarily serves to keep the inner surface smooth to protect the animal’s tissues against parasites and other debris. Another example of this are the pearls formed inside oysters.

ages 10+

Background Information:

Materials:

Steps:

Why do animals have colors?What makes an animal colorful or shimmery?

Iridescence

Global Museum 2

Slideshow ImagesClear nail polishBlack strips of paperShallow dish of water

Materials:

Steps: 1. Why do you think some animals are colorful? Share your thoughts with a classmate, teacher, or guardian.

2. Use the slideshow images to learn about color in the animal kingdom. Where do different animals get their color?

3. Take a close look at the photos of the inside of a red abalone shell. What makes the shell shimmer?

4. Time to create your own iridescence! Gather your materials and fill a shallow dish with about an inch of water.

5. Open your bottle of clear nail polish and touch the tip of the brush to the water, allowing a drop of polish to spread over the water's surface.

6. Take a strip of black paper and gently immerse part of it in the water, allowing the nail polish layer to wrap around the paper.

7. Let dry. Rotate your iridescent paper in the light. What do you notice? What colors do you see? Does it remind you of other iridescent things you've seen?

© Gina Caprari


Color in the Animal Kingdom

The two main ways animals make color: ― Pigment ― Structure

Take a look at the Gouldian Finches in this photo. How many colors can you find?

© Kym Nicolson

Pigment: Carotenoids

Pigments are colors that an animal makes.

Northern cardinals get their red coloration from pigments called carotenoids.

© Austin Hess

Pigment: Melanin

The black color on a seagull’s wingtips comes from melanin, the same pigment that gives us humans our range in skin tones!

© Zack Abbey

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Structural Color

Besides pigments, color can also be produced based on the microscopic shape of an animal’s tissues.

The shimmering blue color of a Morpho butterfly’s wings comes from the shape of the scales.

© Soh Kam Yung

Nacre

Iridescence is another type of structural color, caused by the way light interacts with the animal.

The inside of an abalone’s shell has an iridescent coating called nacre (or mother-of-pearl). The abalone builds this strong coating using minerals from the seawater.

© Giovanni Rapacciuolo

Iridescence

Where else have you seen iridescence?

Many shelled animals have iridescence on the inside, like the mussel in this photo, but other animals have their iridescence on the outside, like the male peacock's shimmery tail feathers.

Why do different animals have iridescence on different parts of their bodies? Why do you think an abalone's shell is iridescent?

© Kathryn Papoulias


Craft Materials

It's time to create your own iridescence! Gather your materials:

― Shallow dish filled with about an inch of water

― Black paper, cut into strips ― Clear nail polish


Step One

Touch the tip of your nail polish brush to the surface of the water, allowing a drop of polish to spread.


Step Two

Gently immerse your strip of paper in the water, letting the nail polish wrap around the paper.


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Step Three

Repeat as many times as you'd like and let the strips of paper dry. You may need to replace the water between paper strips.

Hold your paper up to the light. What do you notice as you turn the paper?

Use your iridescent paper strips as bookmarks or save them for a papier-mâché abalone craft in a future lesson!


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― Doucet, Stéphanie M, and Melissa G Meadows. 2009. “Iridescence: A Functional Perspective.” Journal of The Royal Society Interface 6 (suppl_2): S115–32. https://doi.org/10.1098/rsif.2008.0395.focus

― “Wing scales cause light to diffract and interfere” from the Biomimicry Institute via AskNature.org https://asknature.org/strategy/wing-scales-cause-light-to-diffract-and-interfere/

― Snow, M. R., and A. Pring. 2005. “The Mineralogical Microstructure of Shells: Part 2. The Iridescence Colors of Abalone Shells.” American Mineralogist 90 (11–12): 1705–11. https://doi.org/10.2138/am.2005.1788

― “Secret to Abalone Shell Strength Revealed” by Corey Binns on Live Science. https://www.livescience.com/1694-secret-abalone-shell-strength-revealed.html

― “How Birds Make Colorful Feathers” from the Cornell Lab of Ornithology via Bird Academy https://academy.allaboutbirds.org/how-birds-make-colorful-feathers/

― Image Attributions: 1: Gina Caprari, via The Global Museum 2-6: Various photographers, via iNaturalist.org 7-11: Kathryn Papoulias, via The Global Museum

― Save your iridescent paper strips! You can use them for the next craft, as bookmarks around the house, or turn them into hanging decorations inside windows.

― Where can you find iridescence in your neighborhood? If you live near the beach, see if you can find any mole crab shells in the sand along the water’s edge. Gently rinse them in the water to remove any sand and notice how they shimmer. Like abalone, the inner surface of mole crab shells is iridescent. Go on an iridescent scavenger hunt and see how many other shimmery and shiny things you can find - they don’t all have to be animals!

― Want to learn about coloration in animals in further detail? Read on! Animals produce color through the interaction of two systems: chemical and structural. Chemical color includes pigmentation, chromatophores, and bioluminescence. Pigments are the colors that an animal makes, such as melanin that gives us humans our skin color, or colors they ingest, such as carotenoids from brine shrimp that make flamingo feathers bright pink. Chromatophores are specialized cells that change shape and move pigments to help the animal change color, like an octopus changing color to camouflage in its environment. Bioluminescence is defined as the production of light in an organism thanks to a chemical reaction. A great local place to look for bioluminescence is Tomales Bay. On clear, calm nights, you can see bright blue bursts of light as the waves hit the shore coming from microscopic plankton called dinoflagellates. Structural color, on the other hand, comes not from the absorption of certain wavelengths of light like in a pigment but rather from the diffraction, reflection, or scattering of the light. This structural color can cause iridescence, like the shimmering pink of an Anna’s hummingbird throat, and create the brilliant blue coloration in bird feathers.

References & Further Learning:

Extension:

Investigating Iridescence

Global Museum 8

Reflect on what you've learned. What is your favorite thing you learned? What are you still curious about? Add your notes and observations about this lesson and activity here.

Notes:

lesson 2: investigating iridescence

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