Clearing reagents remove the alcohol and make the tissue receptive to the infiltration media (paraffin). Clearants also make the tissue transparent or clear, hence the name "clearant." Transparency is grossly evident in fatty tissue. Clearants or dealcoholization agents must be miscible with both the dehydrant and paraffin. Although various clearants have been used in the past, the most widely accepted clearing agent is xylene. Clearing is most often completed at room temperature.
As with the alcohols, clearing agents can act rapidly on tissue, causing it to become stiff and brittle. However, insufficient time in a clearing agent will prevent the tissue from infiltrating properly by paraffin, leaving the specimen soft and mushy. Xylene is a commonly used clearing agent. It is miscible with alcohols as well as paraffins but is not miscible with aqueous fixatives. Xylene is intolerant of any water left in the tissue and will not prepare the tissue for paraffin infiltration if dehydration is not complete.
