Back in the old days, when paraffins were personal mixtures of various waxes
including that sticky stuff from bees, histologists who moved from Maine to
Florida had to reformulate in order to be able to cut proper sections.  With
the invention of buildings without openable windows (which were invented by
the refrigeration industry), all buildings came to be air conditioned and
Paraplast was the result (John Kiernan will have a much more serious entry
for this essay contest).  When there came a call for automatic processing
from those Moms who had the night shift in the lab, the paraffin pots were
no longer maintained in closely regulated ovens, but instead in converted
metal coffee pots.  In these, when the temp was set to 60, it meant that the
temperature range would vary from 50-70 depending on which part of the heat
cycle was active, on or off.

Indeed, the issue is with cutting, but even more with cooking.  My first
paraffin bath consisted of three tall, 600ml beakers enclosed half-way up by
shelves of copper which were part of the copper heating chamber.  Heat was
provided by incandescent bulbs such that only a little less than the upper
half of the paraffin was melted.  Infiltration took place at the interface
between the melted and solid paraffin - i.e., at the melting point of the
mixture.  If the bulbs were too hot, then the interface would fall below the
shelves - still at the melting point.  56 degrees was what I measured in the
material we used at that interface.  60 degrees were too hot.  We have all
gotten used to paraffin that melts at 56 degrees being held at 60.  The
melting point should be on the package in which the Paraplast is delivered.
If you have the right processor, it can likely be set at a temperature lower
than 60.  I wasn't able to do any better than that standard setting on my
old Autotechnicon - when I used it.

Hope this helps,

Fred Monson
Frederick C. Monson, PhD
Center for Advanced Scientific Imaging
Geology-Astronomy
West Chester University of Pennsylvania
Schmucker Science Center II
South Church street & Rosedale Avenue
West Chester, PA, 19383, USA
Phone:  610-738-0437
FAX:  610-738-0437
eMail:  fmonson@wcupa.edu
West Chester Boro:  http://www.west-chester.com/
CASI:  http://darwin.wcupa.edu/casi/
WCUPA_Visitors:  http://www.wcupa.edu/_visitors/


Determine the melting point of your paraffin mixture.  You can add to it to
increase or decrease that value.  

-----Original Message-----
From: Ross Stapf [mailto:rstapf@adventisthealthcare.com]
Sent: Wednesday, October 16, 2002 4:05 PM
To: histonet@pathology.swmed.edu
Subject: Paraffin temp for immuno's


Hi everyone:

I was reading through Diagnostic Immunohistochemistry by Dabbs and came
across a comment that paraffin temperatures should not exceed 56 degrees
when doing immuno's on the tissue later.

We have been trying to standardize our methods for optimal immuno results.
We have the occasional case where the staining is not as expected.  We are
trying to eliminate as many of these problems as possible.  Is the paraffin
temp really that important?  I am beginning to wonder if this is one of the
reasons for those cases that should, but just don't stain positive. 

  We have been using Paraplast and Paraplast xtra for over 10 years at 60
degrees.  If I do experiment with a paraffin with a lower melting point,
what can I expect?  Will my techs have a harder time cutting the blocks?
Will I need to increase my infiltration times?

Turn around time is very important, I don't want techs complaining that they
can't get good routine sections just to possibly fix an immuno variable.
Also from my research so far the lower melting point paraffin is more
expensive.

Basically has anybody made a change in paraffin for this reason, and was it
worth it?

Ross Stapf
Histology Supervisor
Washington Adventist Hospital
Takoma Park MD