Forensic microscopy ‐ a basic method of microtraces examination

Abstract

Microscopy constitutes one of the pillars in forensic investigation of traces and samples from a crime scene. Currently, among classic methods of the examination of microtraces using particularly visible radiation is so‐called optical microscopy, be it in the mode of incident light or transmitted light. Simple polarized microscopy can lead an experienced expert to identification of objects. In some cases, it is necessary for trace or sample identification to use also combination with fluorescent microscopy. Electron microscopy and microanalysis belong to crucial applications in investigation traces from crime scene in forensic practise. SEM with EDS/WSD allow a rapid screening and gaining initial information for a wide range traces, including a view of their surface and evaluation of morphology. Microscopic methods are widely employed to analyse of so‐called “microtrases”, it means latent traces (latents), unperceivable by naked eye, but always related to a criminal case. They can involve gunshot residues (GSR) and post‐blast residues (PBR), soils and mineral grains. Microscopy is further applied also in other fields ‐ for example in examinations of handwriting strokes (intersecting lines), biology (morphological evaluation of bio objects), ballistics (composition of bullets), etc. Investigation of paints and pigments is another important field. Each of these used microscopic methods have their advantages and disadvantages, a great asset of optical microscopy is a view and assessment of samples in their natural colours. By methods of optical microscopy we can not only observe morphology of the surface and possible visible marks, but we can also study stratigraphy in samples of paints and pigment in colours of individual layers, which are important features for comparison. Electron microscopy allows to image traces or samples in the shades of grey, however, its options to discriminate and at the same time possibilities of spectral microanalysis are essential for an analysis. A further significant field of the use of microscopic and spectroscopic forensic methods is the detection of forgeries of works of art. Qualification of crimes includes a wide range of violations of the law, from an illegal export of works of art, determination of the ownership right, theft of an artwork, to a fraudulent production of forgeries of prominent authors and their introduction to sale. Thanks to a combined use of microscopic and spectral techniques, it is possible to collect key arguments for comparative analysis of the applied materials, assess morphological and structural marks of pigments, to identify bonding agents and judge painter's technique of the work. In the Czech Republic, forgeries of outstanding Czech artists of the 20 th century are encountered most frequently, such as those of Jan Zrzavý, Emil Filla, Josef Čapek and Pravoslav Kotík. In 2007, two paintings of Pravoslav Kotik with a similar theme appeared on the Czech market that sparked controversy over the authenticity of both artworks and subsequently the whole counterfeiting and with it associated trafficking practices were revealed. The proposed contribution deals with comparative microscopic studies of pigments taken from of works of art. From other microscopic applications, microscopic and spectroscopic forensic methods are important in assessing fragments of car paints found at a crime scene.