[Histonet] More on hard paraffin additive - long discussion

[Gayle Callis]

   Hi Sarah,
   Possibly  could  be the answer.   But your question "Wouldn't paraffin
   hardness  be  a factor of melting point, with the higher melting point
   being  the  harder paraffin?" doesn't seem the case with harder Tissue
   Prep   2.   m.p.  55C  -  57C!     Every  manufacturer  has  different
   additives,  and  depending  on  what  they use, different resins, etc,
   melting  points really vary all over the place. Consequently,  I don't
   think higher mp necessarily means harder paraffin.
   We  use  Tissue  Prep  2  bone here (can either embed after using your
   regular,    favorite   paraffin   in  processor  for  infiltration  OR
   infiltrate  and  embed  in  the Tissue Prep 2 (the ideal situation for
   labs working with large volume of bone).
   We prefer to NOT have the infiltration temperature above 60C for bone,
   with longer processing - higher temp to maintain melted paraffin tends
   to  really  dry out and harden bone. This is probably a combination of
   type of clearant used, length of time in dehydrants, long exposures to
   heat  of  paraffin.     When  we  infiltrate  with Tissue Prep 2 , the
   temperature  is  set  at  58C   with  alternating  vacuum and pressure
   (VIP).   We  avoid  mp  above  60C  just  because  these paraffins are
   generally  infiltrated  at  that higher temperature.   I personally do
   not  like 62C for infiltration of bone. I will opt for lower temp (60C
   and  lower)  particularly  with  3 - 4 changes of paraffin at 58C at 2
   hours  per  change  for larger bone samples.  One paraffin combination
   used   for   years,  before  using  Tissue  Prep  2,  was  Surgipath's
   Infiltration   medium  (separate  in  processor)  and  then  Embedding
   medium.   I  don't  think  it  was  necessarily a harder paraffin, but
   controlling   decalcification  and  processing,  we  had  superb  bone
   sections and was excellent for 1 to 2 um kidney biopsy sections.
   We  have  found  we could use just about any paraffin for bone work IF
   all  else  is  in  place  e.g.  decalcification and processing issues.
   Harder  paraffin  is  certainly  a  bonus, but not always an available
   choice  if  you  do  not  routinely like it for soft tissues.  At this
   point we infiltrate with Tissue Prep, and embed in Tissue Prep 2 which
   works  fine for whole mouse heads, mouse paws, femurs, tibias, hamster
   upper  nasal  turbinates  with partial skull, whole rat heads, femurs,
   tibias.
   If  I  find reference on piccolyte, I will let you know, it was a long
   way  back,  probably  in 1980's.  When we used this, we had a paraffin
   that  looked  like hockey pucks, from Scientific Products - whew, that
   over  30  years  ago.  The little hockey pucks didn't have much in the
   way  of additive at that time.  It was a tedious, timely, messy job to
   melt,  stir piccolyte into paraffin, and then filter.  If you can find
   a hard paraffin that works for you, buy it!