The blocks are then hardened in a drying oven. Over several days the water in the sediment is removed by repeatedly adding and removing acetone. When the water is virtually gone, the process is repeated with epoxy exchanges. The sections are then cured in the drying oven. They are lifted out, then flash frozen in liquid nitrogen, hindering the formation of ice crystals.
Samples are next freeze-dried.
Low viscosity epoxy resin is poured over the sample under vacuum, then allowed to set and cured in a drying oven. The exchange method gives the least distortion in the sediments and also allows sediment to be cut on an angle to give a good overlap. However, it is slow, involves much handling time, and generates a large amount of flammable and toxic chemical waste. The freeze-dry method has minimal handling time and almost no chemical waste. Removing the thin slices from cut core surfaces is an art.