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FIBERS - PART ONE: THE NATURAL LOOK

© Elizabeth Becka Lansky

Technology marches inexorably onward, but it is to the benefit of forensic scientists that we are not yet living in the sterile, steel and Formica world of 2001. Humans prefer to touch something a little softer, and fabrics are still very much among us. We are surrounded by upholstery, clothing, towels, and carpets—and so are victims and murderers. They can’t help it, unless they want to walk around naked. All fabric is composed of bundles of threads, woven together in a way to make the fabric soft, fluffy, strong, breathable, smooth or whatever else the manufacturer wants. Entire books have been written to cover the basics of this process. A piece of fabric found at the scene can be compared to the suspect’s clothing by its weave pattern, twist of the threads, fiber composition, etc. But take it from me, it’s a rare case indeed when a CSI stumbles on a piece of fabric, or even a thread. Most of the time you’re lucky if you even get fibers.

Fibers are the most basic unit of material the way the atom is the most basic unit of matter, and they are separated into two categories: natural and synthetic. Rayon actually falls between the two categories since it is reconstituted cotton, but is generally considered a natural fiber.

Natural fibers are those that are produced by plants or animals—wool, cotton, silk, hemp, linen. Synthetic fibers start as chemical mixtures and are pulled into long fibers through a sieve. We’ll deal with those in the next article. The most common fiber, period, is cotton. Under a microscope, it looks like flattened tubes, which twist and bend. Any fiber expert will identify it in a heartbeat. Silk also appears tubular, but doesn’t twist as much. Of course, fiber experts will have slides upon slides of samples of these fibers, to compare with the unknown fibers—but once they know cotton, they won’t need a reference to identify it. Wool looks like what it is—animal hair, with overlapping scales. Fibers used to be lumped with hairs, so that the same expert examined both. However, with the compartmentalizing of large state labs and the phasing out of hair comparisons, it is now just as likely that a fiber expert will deal only with fibers.

Once an expert identifies what kind of fiber it is, they can compare the color of the known and unknown fibers. Because all natural products vary-- no two natural fibers will be identical, in the same way no two flowers are identical—they cannot be tested by solubility or infrared spectroscopy as synthetic fibers can. Therefore their conclusion is: This is blue cotton, and the suspect’s shirt was blue cotton, and the blue appears to be the same or similar shade. And that’s all I’ve got to say about that.

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