Simplified Sample Embedding and Polishing Methods for Preparing Hydrophilic, Fragile, or Solvent-Susceptible Materials for Thin Sections for Microscopic Analyses

In the preparation of thin sections for microscopy, embedding and polishing processes in particular can change the composition and morphologies of samples. Soils and ashes are very fragile and solvent-susceptible, and appropriate sample preparation procedures have not been well-established. To improve the existing preparation methods and make them easier and faster, we embedded freeze-dried blocks, polished, and then examined these thin-section samples using polarization microscopy, laser microscopy, and field emission scanning electron microscopy with energy-dispersive X-ray spectrometry, and electron backscattered diffraction (EBSD). Appropriate thin-section samples can be prepared by: (1) rinsing with acetone and then embedding with Spurr resin along with repeated evacuation and ventilation, rather than conventional dehydration/replacement; (2) polishing using silicon carbide paper and diamond slurries, and then wiping with a cloth and a synthetic oil; and (3) slightly rinsing with 100% ethanol to remove the oil. The preparation method minimized contamination and pores, and showed flat surfaces and sometimes EBSD patterns. Freeze-drying has been claimed to cause the development of cracks due to ice crystal formation upon freezing, however, our method not only overcomes such problems for microscopic observation but saves substantial time, taking only 2 days in total to process a specimen, and requiring less than 1 g of resin and ~1 g of sample.