RE: [Histonet] Plastic Embedding Molds

From:"Bartlett, Jeanine"

We use both in our lab and I prefer the metal molds for the reasons Tim listed.  However, Tim mentioned one drawback of metal molds being the time required daily to clean them.  Honestly, I find that cleaning and treating once a year is plenty, if that often.  When I get new molds I spray them with any spray-on mold release (not the kind you have to soak the molds in) and that is usually sufficient.  When I treat some older ones that have been previously used I run them through the clean cycle of the VIP (I know that is a no-no but I don't do it often!) and then apply the spray. I do not embed daily but when I was working at a small local hospital years ago where I did embed daily I found cleaning/spraying twice a year was sufficient.  So I don't think the time involved in cleaning/handling metal molds is an issue at all.
Just my point of view!
Jeanine Bartlett, HT(ASCP)
Centers for Disease Control
Infectious Disease Pathology Activity
1600 Clifton Road, MS/G-32
Atlanta, GA 30333
-----Original Message-----
From: [] On Behalf Of Morken, Tim - Labvision
Sent: Tuesday, December 16, 2003 12:59 PM
Subject: RE: [Histonet] Plastic Embedding Molds

Dr. Hessler wrote: "...what advantages do these have over traditional steel other than you don't clean them? As steel basically has an unlimited lifespan, are the disposable molds really cost effective in a clinical laboratory."


Plastic molds:


Very high cost (although they can be reused for a while - just don't store in the heated space of the embedding center or they get warped)

Hard to orient fragments due to some kind of electrostatic forces that move the pieces around.

Slow to cool - again hard to work with small fragments and skin when you want to orient them a certain way. (though some may see as an advantage)

Not as flat on the face as metal, so more trimming - bad for very small specimens.

Do not hold heat the way metal does, so cools faster on the sides when time is spent orienting tissue. I see many more mis-oriented tissues in plastic molds, and mis-oriented mold/cassette problems (block face is mis-oriented to the cassette back, which means the block face is at an angle in the microtome chuck...= more trimming).



The sides of the mold are more vertical than the metal mold so a bit easier to cut (smaller face, sharper edge)

Easy to take off the block (metal molds are often difficult to remove)





Very low cost, last forever

Flat face

Cool fast



Sometimes difficult to remove - use mold release (but that does take time and requires cleaning the molds daily in xylene/alcohol - we put them in the tissue processor and run the clean cycle)

Cracked blocks? I haven't seen that as a problem. It is mainly in large blocks. You can put them on a piece of paper over the cooling plate to avoid that.


It seems the only real advantage of the plastic is the shorter time spent taking the mold off the block and avoiding the time it takes to clean the metal ones (about 15 min/day max)

If I was paying the bills I wouldn't get the plastic - they are far more expensive and do not give as good quality face as the metal.

But...I haven't done a cost analysis of the plastic molds vs time spent to clean metal molds and then soak in mold release every day.



Tim Morken


-----Original Message-----
From: Richard Hessler []
Tuesday, December 16, 2003 7:56 AM
Subject: [Histonet] Plastic Embedding Molds


I would like advise about disposable plastic embedding molds. Was wondering if any clinical labs had experienced problems with delays and uneven tissue alignment due to static and slow heat transfer. Also, what advantages do these have over traditional steel other than you don't clean them? As steel basically has an unlimited lifespan, are the disposable molds really cost effective in a clinical laboratory.




Richard B Hessler, MD
Chief, Section of Anatomic Pathology
Associate Professor of Pathology and Neurology
Medical College of Georgia

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