[Histonet] hard vs. soft paraffin

[Philip Muscarella]

Aside from the answers given, we have found that producing a continuous
ribbon of paraffin mainly depends on the temperature of the block, and the
blade. The hardness and size of the object may of course affect the ribbon,
but if the object is small, and completely infiltrated, the effect is
practically negligible. If the temperature of the knife and block is made
sufficiently low, very thin sections can be cut without excessively
compressing the object, regardless of the melting point of the paraffin. If
the microtome is set for thinner sections without lowering the temperature
of the knife and block, the sections are compressed more and more as they
are made thinner, until the tissues are crushed out of all likeness to their
original. The simplest way to cool the blade that we have found, is to
simply spray the blade with fast freeze just before cutting.

When problems with compression still exist aside from the obvious (cutting
too fast, blocks not kept cold until just before cutting etc.), one might
adjust the clearance angle of the blade. You can obtain a proper angle by
systematically decreasing the clearance angle until you find an optimal
position. 

Philip P. Muscarella, H.T.
Histology Laboratory
Dr. Malott M.D. - Dermatology
Kihei, Maui, Hawaii


-----Original Message-----
From: histonet-bounces <@t> lists.utsouthwestern.edu
[mailto:histonet-bounces <@t> lists.utsouthwestern.edu] On Behalf Of Rene J Buesa
Sent: Monday, March 19, 2012 10:47 AM
To: 'histonet <@t> lists.utsouthwestern.edu'; Clare Thornton
Subject: Re: [Histonet] hard vs. soft paraffin

Besides some additives that all paraffins have, "hard" paraffin is one that,
as you point out, has a melting point (MP) of about 63ºC. There are even
"harder" paraffins with MP of up to 70ºC and usually are more white in
color.
The "normal" paraffin has a MP of about 53-55ºC, and soft paraffins are of
less than 50ºC, usually about 43-45ºC.
The temperature of the water bath has nothing to do for paraffins above 50ºC
and is usually always at about 45ºC.
Sections of very soft paraffins should be extended in water baths at room
temperature and usually are very difficult to work with.
The harder the specimen, the higher the MP of the paraffin should be. Plant
materials, specially twigs and branches to be cut transversely, require the
hardest of the paraffins.
Ideally the paraffin should have a hardness to coincide with that of the
tissue.
René J.

--- On Mon, 3/19/12, Clare Thornton <CThornton <@t> dahlchase.com> wrote:


From: Clare Thornton <CThornton <@t> dahlchase.com>
Subject: [Histonet] hard vs. soft paraffin
To: "'histonet <@t> lists.utsouthwestern.edu'"
<histonet <@t> lists.utsouthwestern.edu>
Date: Monday, March 19, 2012, 2:13 PM


What constitutes "hard" paraffin vs. "soft" paraffin?  Is it just melting
point?  What are the characteristics of hard and soft paraffins?  How does
water bath temperature play a role?  Which is preferable for avoiding
compression of tissue?

thanks,
Clare

Clare J. Thornton, HTL(ASCP), QIHC
Assistant Histology Supervisor
Dahl-Chase Diagnostic Services
417 State Street, Suite 540
Bangor, ME 04401
cthornton <@t> dahlchase.com

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