The most significant step in examining a fiber for comparison is performing a microscopic comparison for the color and the diameter of the fiber, by using a comparison microscope. If the color and the diameter are not similar, then the fibers are not a match. Other morphological features that could be present to aid in the comparison are lengthwise striations on the surface of some fibers and the pitting of the fiber’s surface with DE lustering particles ( usually titanium dioxide) added in the manufacturing process to reduce shine. The cross sectional shape of a fiber can also help identify a fiber. When comparing two fibers under a microscope, the fibers can appear to have the same exact color, but the compositional differences in the dyes will prove that they are not the same.
Textile fibers are often mixed with a variety of dyes in order to achieve a particular shade or color. The significance of a fiber comparison is enhanced when the forensic examiner can show that the questioned and standard / reference fibers have the same dye composition . The colors of various fibers can be compared by using visible light micro spectrophotometer. Visible light micro spectrophotometer is an efficient way for analysts to properly compare the colors of fibers by using spectral patterns. Visible light micro spectrophotometer is useful for examining fibers that are as small as one millimeter or less.
There is no damage done to the fibers when they are examined using visible light micro spectrophotometer. A chromatographic isolation of the dye constituents can give the analyst a more detailed analysis of the dye composition in the fiber. To accomplish this, small strands of fibers are compared for dye content by first extracting the dye off each fiber with a suitable solvent and then spotting the dye solution onto a thin layer chromatography plate . After the dye components and fibers have been separated on the thin layer plate, they are then compared side by side to see are they the same. The fibers must have the same chemical composition before they can be considered to be the same.
Fibers can often have the same properties, but can differ in physical shape or appearance. Textile chemists have many different methods of determining the class of a fiber. However, unlike the textile chemist, the criminalist frequently does not have the luxury of having a substantial quantity of fabric to work with and must therefore select tests that will yield the most information with the least amount of material . Criminalist often have very little to work with when examining fibers. The fibers can be as small as a single strand from a sweater.
If the investigator is not specifically searching for fiber evidence, it can be easily overlooked because it can not be seen easily with the naked eye. Relevant articles of clothing should be packaged