Microscopes and Crystals - National High Magnetic Field Laboratory

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ACTIVITY 16: USING MICROSCOPES TO INVESTIGATE BIREFRINGENCE m6: Microscopes and Crystals Photomicrography is a technique that involves using polarized lenses and cameras to observe birefringence in crystals. This technique is used at the National High Magnetic Field Laboratory (NHMFL) by Mike Davidson whose images are used on ties, scarves, exercise wear, book covers, folders, and many other items. The beautiful images that have been created using this technique can be accessed at the following web site: http://micro.magnet.fsu.edu/. There is a scientific application as well as an artistic application. The process has been used for a long while by biologists and in the medical sciences. Interest in semiconductors, which directly relates to the work at the NHMFL, has required new tools to explore the surface features of new materials. In general, photomicroscopy is used as a tool to examine the surface of crystallized samples. In this Activity, you and your students will be making crystals and examining them using the naked eye and the compound light microscope. You will also be looking at the crystals using polarized light film that will allow you to view the many colors in birefringent crystals, like Epsom salt crystals or copper sulfate crystals. MATERIALS: $ Field microscopes or other compound light microscopes $ Glass slides $ Epsom salt, copper sulfate, or vitamin C powder $ Warm water $ Polarizers $ Science Notebook WHAT WILL THE STUDENTS DO? 1. Students will make crystals (see Activity 14, this Module) using Epsom salts, copper sulfate, or vitamin C powder. *Encourage students to try using different types of solvents other than water. Rubbing alcohol and acetone (fingernail polish remover) may be used and students might get better quality crystals. 2. Students will be observing crystals with their eyes and using their field microscopes. Each observation is structured and each sample is represented with a drawing in students’ Science Notebooks (see student page). 3. Students will be investigating the various crystals using the polarizers and the field microscopes. SCIENCE, OPTICS & YOU GUIDEBOOK - 152 -
ACTIVITY 16: USING MICROSCOPES TO INVESTIGATE BIREFRINGENCE m6: Microscopes and Crystals How To Use the Polarizers: 1. Place one polarizer beneath the slide 2. Place the slide containing the crystal sample and the polarizer on the stage of the microscope. 3. Place the other polarizer on top of the eyepiece of the field microscope. 4. While looking at the different crystals, rotate the lens on top of the eyepiece. Notice and record which crystals are birefringent. 5. Crystals that are birefringent will produce beautiful colors as the eyepiece polarizer is rotated. Remember, not all of the crystals that the students made will be birefringent. Those that are not birefringent will appear to be clear when viewed through the polarizers rather than exhibiting many colors. DEMONSTRATION: Take a clear plastic cup and place it on an overhead projector. Put about an inch of Karo syrup in the bottom of the cup. Turn the projector on and students will see colors projected on the screen. This is because plastic is birefringent. Karo syrup is the medium used to display this property. Encourage students to try other media and record their observations. EXTENSIONS: Narrative Writing. Each of us has seen the beauty of crystals after they are polished and cut and made into jewelry. Before you begin writing, think about a time that you saw a lovely piece of jewelry that was special to someone. Now write a story about that special piece of jewelry and why it was special. Reading. Read aloud poems from Once Upon Ice and Other Frozen Poems by Jane Yolen (ISBN 1-56397-408-8) and have students compare the crystals they made with ice crystals. Then have students write poems about the crystal shapes they observed. Research. Students can research birthstones and other gemstones. Encourage students to research myths and legends that have been written and/or passed down from generation to generation regarding gemstones. Have them identify their birthstones and share with the class. SCIENCE, OPTICS & YOU GUIDEBOOK - 153 -
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Microscopes and Crystals - National High Magnetic Field Laboratory

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