Contributed by Jeremy Morris
Cosmetics are extensively used in society but commonly overlooked as a source of trace evidence. They include a wide variety of products including foundation, concealers, blush, mascara, lipstick, eyeshadow, and more. In a forensic context, cosmetics can be forms of trace evidence transferred between individuals or from an individual onto an object. Additionally, cosmetics can be used to conceal injuries on a victim.
Cosmetics are manufactured from a variety of materials routinely encountered in other sub-disciplines of trace evidence. Facial products routinely contain titanium dioxide, iron oxides, kaolin clay, talc, and mica. These same minerals can also be found in paint and tape samples; however, because cosmetics are designed to be applied to the body, additional processing techniques are applied to the minerals so they can meet stricter regulatory requirements. These additional processing techniques can alter some microscopic or chemical features of the materials.
The forensic analysis of cosmetics may include the identification or comparison of samples. Identifying a substance as a cosmetic may involve the identification of numerous materials and recognizing their combination is consistent with cosmetic products. Comparison of two samples presents its own challenges. Different products may contain the same materials but the materials may be mixed in different quantities (e.g., different shades of foundation) or the materials may have different physical properties (e.g., different sizes of mica flakes for sheen or glitter appearances). Additionally, the known standards may contain liquid components, sometimes in significant quantities, which are not present in the questioned sample due to either evaporation or absorption into the skin.
The analytical approach for cosmetics involves traditional trace evidence techniques. Infrared spectroscopy and gas chromatography-mass spectrometry can identify the organic components of the material. Infrared spectroscopy can also be used to identify some of the inorganic components. Polarized light microscopy can be used to identify and characterize many of the components within the material. Scanning electron microscopy coupled with an energy dispersive detector can both visualize the materials but also obtain the specific elemental composition of individual particles. This is especially useful in differentiating samples containing natural mica with those containing synthetic mica, commonly used as a glitter.
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