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What is the color? Is there any pleochroism? What is the diameter?
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Anisotropic fiber
| YES
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With the analyzer on, does the fiber go to extinction?
| NO
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Isotropic fiber
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Positive: n parallel > n perpendicular
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If first order colors are seen, what is the sign of elongation?
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With the analyzer on, what interference colors are seen (first order or higher)?
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Negative: n perpendicular > n parallel
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What is the refractive index in both the parallel and perpendicular directions? Look at relief and Becke lines in several oils until and ID can be made.
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Animal hair
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YES
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Cotton
| YES
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Do the fibers appear twisted?
| NO
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Are the fibers straight along the entire length?
| YES
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Are any surface patterns evident?
| YES
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Do the patterns appear to be surface scales?
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NO
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NO
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Synthetic fiber
| YES
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Are the fibers uniform and featureless along the length?
| NO
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Can cell walls be seen on the fibers?
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Do the patterns appear to be longitudinal striations?
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NO
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YES
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YES
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Textured synthetic or silk
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Vegetable fiber
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Viscose
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