[Histonet] Molds- cold vs warm

Jay Lundgren jaylundgren at gmail.com
Fri Sep 9 16:36:44 CDT 2022

Whoever is telling you to use cold molds needs to go back to clown college.

That is totally, 100%, absolutely, wrong.

There is some debate as to embed "wet" (cassettes submerged in paraffin
bath) or "dry", and I will accept either, as mostly a matter of personal
preference.  BUT, in both of these cases, the molds are hot.

I have been a Histotech for five decades, trained at Armed Forces Institute
of Pathology (back when that used to mean something) and I have NEVER seen
anyone using cold molds.

It is a guaranteed way to get cold fractures and cracks in your blocks, or
to pop tissue out when you are cutting, which might be irretrievable. Just
think how much time all those re-embedded blocks are going to save you!

Also, you won't be able to easily re-position specimens in the block, to
put them "on edge" or "on end", for example.  The tissue will instantly
stick to the cold mold.  And if you want to re-position it, guess what,
you'll have to warm the mold up to get the tissue unstuck.  How's that
(non-existent anyway) time savings now?

If you want to prove to whatever jackass suggested this that they are
wrong, get a big stack of every histopathology textbook you can find.
There is nothing in any of them talking about paraffin embedding with cold

As a matter of fact, every single textbook will specify molds at the same
temp as paraffin.

Anyway, it doesn't even make sense, thermodynamically.  Heat travels from
hot to cold.  Those "cold" molds will be the same temperature as the
paraffin, almost instantly. Did it take a tiny amount of heat out of the
hot paraffin? Yes, but not enough to noticeably cool the blocks faster. The
amount of heat from the paraffin used to warm the mold is trivial compared
to the total heat of the system. That's why cold plates have huge, noisy
refrigeration units.  You can't argue with thermodynamics.

If you are having trouble getting your blocks to release, use mold
release!  Viola!  https://www.statlab.com. I used to think it was
superfluous, but now I consider it compulsory.  This is probably the answer
to most of your issues.

I don't know who is suggesting using cold molds, but I can pretty much
guarantee that it's a pathologist who thinks his slides are taking too
long, and knows nothing about histopathology, or a lab manager, who knows
nothing about histopathology.  This next part is directly to them.

To Whoever Suggested Cold Molds:  The answer to getting your slides out
quicker is buying more equipment and hiring more techs, and holding
everyone to standards (30 blocks/hr cutting, 60 blocks/hr embedding).
Making nonsensical, uninformed suggestions only exposes your ignorance.

Please feel free to show them this reply.


Jay A. Lundgren, M.S., HTL (ASCP)

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