Isopentane is not an embedding medium. OCT (or another comparable brand) is the embedding medium. Isopentane cooled with liquid nitrogen or dry ice is the freezing medium for freezing the liquid OCT into solid blocks.
In sucrose cryoprotection, some people wash out the formalin before going into the first sucrose solution. I find that the sucrose solution itself washes out the formalin quite adequately. You do not wash at all between the different concentrations of sucrose. That would defeat the purpose of using an ascending series of concentrations.
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