Cut Mark Classification With Energy Dispersive X-ray Analysis

Cut marks are preserved records of human activity and are used by anthropologists for a variety of purposes including reconstructing past events. Presently, examination of surface modifications with a dissecting or scanning electron microscope is the most common technique for mark classification. Although appropriate for morphologically typical marks, these methods are subjective and non-applicable to atypical marks. In light of these limitations, the author attempted to develop a method that utilized residual material transferred from a weapon to the bone for classification.

Recent advancements in electron microscopy led to the development of the environmental scanning electron microscope (ESEM) equipped with energy dispersive X-ray analysis (EDX). Analytical capabilities of this microscope include identifying the elemental composition of the surface of fresh bone. In the study, this instrument was used to compare the elemental composition within a cut mark to the elemental composition of an unmarked control area.

The cut marks analyzed in the study were the result of stabbing intravenously euthanized domestic pigs (sus scrofa) with smooth, slightly serrated, and serrated edged knives. The experiment was designed to mimic a forensic event, from stabbing the pigs to leaving them in an open-aired, wooded facility to decompose. Each bone inflicted with a cut mark was collected, washed with ethanol and analyzed with an Emas/Mas SEM equipped with a EDX Robinson Detector. The results on the analysis were statistically evaluated with the t-test and chi-square test using SAS v6.12 statistical program.

Analytical results showed that significantly more carbon was present in the cut marks made with slightly serrated and smooth edged knives than on their respective control surfaces. However, Iron (Fe) and chromium (Cr) which makes up a larger percentage of the composition of stainless steel (≥83.03% and 13%, respectively) than C (.25%), was not detected in any of the marks. The differences in the amounts of C are more likely an artifact of analysis than residual material. Possible reasons for the results include the limitations of EDX when applied to trace elemental analysis of rough surface specimens (such as bone) and the critical quantity of an element needed for detection. Hence, cut mark classification is not possible with EDX given current limitations of the instrument. However, refinements in electron and ion microscopy will overcome the present limitations making future development of a cut mark classification method based on residual material foreseeable.