IMAGING MAZON CREEK FOSSILS USING TEXTURAL AND POLARIZED LIGHTING

Relatively inexpensive macrofossil photographic techniques designed to enhance contrast and emphasize details can dramatically improve the quality of fossil photographs. These include: low-angle, cross-polarized, and ultraviolet lighting; color filters; and submersion of fossils in water and alcohol. Last year we digitized the Field Museum’s type collection of Mazon Creek fossils as part of the museum-wide Grainger Digitization Initiative. We used a Kaiser RS1 camera stand with Kaiser RB 5004 high frequency lights and adjustable lamp arm and used a Canon 50D camera body with a 60mm macro lens. We captured both a cross-polarized and a low-angle lighting image for each specimen. To convert our existing camera station into one capable of taking cross-polarized photographs, I taped a Rosco Cinegel linear light polarizing filter over the lights to create a polarized light source and added a circular polarizing filter to the camera lens. Our conversion totaled less than $100. Using the crossed-polarized lighting setup enhanced the contrast and color saturation of fossil specimens, including highlighting color patterns on insect wings and bristles on polychaete worms. This technique also reduced reflections and produced a flatter light (loss of topographic details). Cross-polarized lighting enhances details by increasing the contrast between fossils and rock matrix, especially with low-contrast fossils such as Burgess Shale specimens or graptolites in black shale. Because polarized light reflects in a more uniform manner from the fossil material than from the surrounding matrix, aligning the polarized filter on the camera lens with the polarized light reflecting from the fossil allows the camera to capture the enhanced contrast between the matrix and the fossil. Lowering the light arm of the camera stand and removing the polarizing filter allowed us to capture low-angle lighting photographs, which captured enhance textural (topographic) details such as venation on insect wings and striations and ribbing on shell material. Both techniques were used on each specimen, and the resulting pair of images provides more details and allows for a better understanding of the fossil specimen than from a single standard photograph with little additional cost or time required.