[Histonet] Microwave drying/paraffin sections from Histonet archives - long but maybe pertinent?

Gayle Callis gcallis <@t> montana.edu
Fri Jan 6 18:07:37 CST 2006

If glass could heated up by microwaves, then why are we able to remove 
pyrex beakers, coplin jars or in our homes, glass pyrex measuring cups 
containing water heated to visual boiling with little skin protection i.e. 
bare hands (although I don't advocate this in home or laboratory, a hot 
mitt is always a good idea!).  However the longer it takes to heat the 
water in my kitchen MW, the hotter the glass becomes over time with the 
transmitted heat.  Some glass containers have gold borders or other 
components(?) that are not microwaveable, with warnings -  but these are 
not glass slides.

The question and discussions on MW drying are numerous, but three messages 
stood out and should be considered if wanting to do this.  The biggest 
concern should be what kind of artifact or tissue section damage is created 
with MW drying?  Histotechnicians have experienced this, per archive 
messaging.  Although MW drying saves time, does it lead to eventual 
problems in staining, diagnosis, etc.?  We tend to dry our slides at lower 
temperatures in an oven i.e. Buessa convection oven method.

I thought these excerpts from a Peggy Wenk message about microwaving 
pertinent, and the way I always understood a MW to work.

Microwaves cause molecules that have a charge (like water or alcohol) to 
align to the wave as it passes. After the wave passes, the charged molecule 
goes back to whatever direction it wants to point, at least until the next 
wave passes by, at which point the charged molecule realigns again. So, you 
have a bunch of charged molecules aligning and becoming randomly arranged,
millions of times a second (frequency of a microwave). While these charged 
are aligning and un-aligning, they are bumping into each other. This causes 
friction, which
causes heat. Which is how aqueous or alcoholic solutions (or your supper) 
heats up.
Now, some things do NOT have charges to them. Like the glass or pyrex or 
plastic in the
coplin jar or casserole dish. So the molecule do NOT move. So there is NO 
friction. Therefore no warming. (The only exception, if you want to 
consider this, is drying slides in the microwave oven. But in this case, 
the water between the slide and the tissue/paraffin section is being 
heated. In this case, it is usually advised to have a beaker of water in 
the back corner of the microwave, so that there is something to absorb the 
microwaves, so that the oven is not harmed.)
Peggy A. Wenk, HTL(ASCP)SLS
William Beaumont Hospital
Royal Oak, MI 48073

On slide drying, there may be some other effects you do not want, like 
introducing artifact to the tissue sections -

Charles.Embrey[SMTP:Charles.Embrey <@t> carle.com]
  Sent:  Wednesday, October 10, 2001 3:43 PM
I have worked at places before that dried slides in the microwave.  In
my own lab I will not.  The microwave tends to overheat during this process
and I saw several burn up.  I was always afraid of fire.  Drying slides in
the microwave also creates interesting artifacts when the water boils under
the tissue.  I just don't like it.  I am sure however that others do and
will probably beat me up over my stand but it's just my personal preference
and experienced opinion. No daggers please  Charles R. Embrey Jr., 
Histology Supervisor
Carle Clinic
Urbana, IL

And from a Microwaving expert:

Subject: Drying paraffin slides
Date: Tue, 02 Apr 2002 12:01:43 -0600
Hi - Just a point of terminology - whether heating slides in an oven,
with forced air, or in the microwave, you are NOT drying the paraffin.
You are drying the layer of water between the paraffin and the slide.
Cheryl Crowder, BA, HTL(ASCP)
Chief Technologist
Department of Pathobiological Sciences
School of Veterinary Medicine
Louisiana State University

Gayle Callis
Research Histopathology Supervisor
Veterinary Molecular Biology
Montana State University - Bozeman
PO Box 173610
Bozeman MT 59717-3610
406 994-6367
406 994-4303 (FAX)

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