[Histonet] Molds- cold vs warm

[Shirley A. Powell]

Well said Jay.
Thanks, 
Shirley Powell


-----Original Message-----
From: Jay Lundgren via Histonet <histonet at lists.utsouthwestern.edu> 
Sent: Friday, September 9, 2022 5:37 PM
To: Naira Margaryan <nmargaryan88 at gmail.com>
Cc: histonet at lists.utsouthwestern.edu
Subject: Re: [Histonet] Molds- cold vs warm

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 molds.

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://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.statlab.com%2F&data=05%7C01%7Cpowell_sa%40mercer.edu%7C84d81a9eddad4ba8159308da92ab72a7%7C4fb34d2889b247109bcc30824d17fc30%7C0%7C0%7C637983562331339740%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=YDxIy7oMkibqOiMnl0D44LCG3XD0oKPY7jFHZBHBrsM%3D&reserved=0. 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.

Sincerely,

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