Instrumedics' Protective Oil ,Cat#PO,  was developed for coating  the frozen
block to protect it from dehydration in long term storage at -80C. The oil
remains a liquid until -10C so that it can be brushed on the frozen block
without melting the tissue. When it is brushed on to the tissue which is
below -10C it freezes and offers the  protection from dehydration which
takes place over time in a freezer.
When the block is to be sectioned the solidified oil coat is trimmed away
when facing off the block to expose the tissue.

Bernic