Using various microscopic techniques, we studied waterlogged archaeological wood of oak (Quercus sp.), ash (Fraxinus sp.) and willow (Salix sp.) that was about 4,500 years old. Thin sections for microscopy were cut manually from frozen wood and by a rotary microtome after embedding into paraffin. We observed them with a light microscope using bright field, polarization, or epi-fluorescence mode. Sections were unstained or stained with combinations of safranin, astra blue, acridine orange, and chrizoidine. We tested the usefulness of methods for wood identification and for assessing the degradation of cell walls. In the cases of oak and ash, a quality cross-section was sufficient for wood identification, larger sections offering an advantage. With willow, all three anatomical sections had to be observed, and due to the degradation of the wood we used a combination of methods. Staining and the use of the epi-fluorescent technique highlighted the anatomical details of the observed wood species. When determining degradation, the specimens embedded in paraffin performed best, as the wood could also be observed at a greater magnification with all the techniques listed. When cutting slides with a rotary microtome, we more frequently detected cell collapse and cell wall lacerations. The method of freezing and manual cutting is the simplest and most rapid, and the slides do not disintegrate as the sections are relatively thick. The method of embedding into paraffin allows us to produce thinner slides, which enables greater magnification and therefore insight into the minute structure. With the polarizing and epi-fluorescence techniques, we can see structures that are not visible by normal light. By using polarization mode, we can see birefringence of cellulose, and epi-fluorescence highlights lignin, which fluoresces.
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