It has been my practice since time immemorial to place blocks 
face down on a tray of ice  - even before "trimming" "facing-off"' 
whatever.  There are always trays of ice ready in the freezer!
The blocks are then returned to the ice awaiting their turn to be 
sectioned (* see below).
The only "regular problem in my labs is that mucin (in salivary 
glands, for example), tends to swell from the surface.  The block is 
easily re-faced - trimmed - immediately before sectioning.
Portions of these glands are invariably less well processed than 
other tissue in a routine programme.  Swollen material can, on 
occasion, protrude from the block surface  The reasons have been 
well covered in these pages before.

This is the important bit.    The reason for using ice - or ice-water - 
is that as the temperature is lowered, so differences in hardness 
become less and less.  The advantages of trying to bring all tissue 
components in the block to a common consistency should speak 
for themselves.  (Forgive the grammar - or lackof it).

* The ice will, of course, be melting all the while and blocks will, 
therefore, be cooled (iced) and soaked.

Russ (in a white coat!)
Russ Allison, 
Dental School
Cardiff
Wales