Editing Histology (section)

==== Paraffin wax ====
[[File:Tissue processing - Embedding station.jpg|thumb|300px|left|Histologic sample being embedded in paraffin wax (Tissue is held at the bottom of a metal mold, and more molten paraffin is poured over it to fill it.)]]

For light microscopy, [[paraffin wax]] is the most frequently used embedding material.<ref name="Bancroft and Stevens, 1982" /><ref name="Wick, 2019" /> Paraffin is immiscible with water, the main constituent of biological tissue, so it must first be removed in a series of dehydration steps.<ref name="Bancroft and Stevens, 1982" /> Samples are transferred through a series of progressively more concentrated [[ethanol]] baths, up to 100% ethanol to remove remaining traces of water.<ref name="Ross and Pawlina, 2016" /><ref name="Bancroft and Stevens, 1982" /> Dehydration is followed by a ''clearing agent'' (typically [[xylene]]<ref name="Wick, 2019" /> although other environmental safe substitutes are in use<ref name="Wick, 2019" />) which removes the alcohol and is [[miscible]] with the wax, finally melted paraffin wax is added to replace the xylene and infiltrate the tissue.<ref name="Ross and Pawlina, 2016" /> In most histology, or histopathology laboratories the dehydration, clearing, and wax infiltration are carried out in ''tissue processors'' which automate this process.<ref name="Wick, 2019" /> Once infiltrated in paraffin, tissues are oriented in molds which are filled with wax; once positioned, the wax is cooled, solidifying the block and tissue.<ref name="Wick, 2019" /><ref name="Bancroft and Stevens, 1982" />