[Histonet] Cracking paraffin blocks

[Hans B Snyder]

Hello Tim,

I also have had this cracking problem in the past but since resolved.
I'm not sure about the specifics of the cracking problem but the cold
plate might have something to do with it.  Our cold plate is set to
-5C and use Paraplast from McCormick Scientific.  Our paraffin is
roughly the same melting temp as yours, so probably not much
difference.

Unfortunately trial and error is apart of our jobs since there is
relatively little uniformity in histology equipment and products. Have
you tried setting the cold plate to a warmer temperature yet?  It's
worth a try and if that doesn't work maybe the paraffin has been
getting too hot.  I know when the paraffin gets too hot, the wax and
plastic separate or break down and cause inconsistencies in the
paraffin.  To test this, take an external thermometer and place inside
the paraffin tank.  Then record the temp every hour for some time.
This will tell you if the tank itself is a consistent temperature.

Also, are the blocks taken off the cold plate and immediately jarred
loose from the mold?  Sometimes when I do this the shock of pried out
of the mold can cause the paraffin to become brittle and break rather
than bend.

Let me know how it goes.

Thank you
Hans B Snyder
Histologistics
60 Prescott Street
Worcester, MA 01605
508-308-7800
hans <@t> histologistics.com


On Fri, Jan 23, 2015 at 9:57 AM, Wheelock, Timothy R.
<twheelock <@t> mclean.harvard.edu> wrote:
> Hi Everyone:
>
> Recently, I purchased the Medite Valida Embedding Center, which I demoed previously without a problem, if I recall right.
> I am having problems now with blocks developing cracks on the cold plate.
> The cracks run either through the wax right next to the specimen, or more frequently, right through the tissue itself.
> I use Surgipath Embedding Media (EM-400).
> The surface of the Valida's cold plate is -14C.
>
> The company has not seen this happening before, but they are looking into this further.
> Also, I had the same problem when I demoed the Thermo-Fisher HistoStar.
> I do not think that this is a problem inherent with any particular machine.
> Has anyone encountered this problem before?
> If so, how did you resolve it?
>
> Is it possible that the -14C cold plate is too cold? Should I warm it up a bit?
> The surface of the Valida cold plate is, I believe, made out of smooth stainless steel.
> My old (24 years) Shandon Embedding Center's  cold plate is made out of cast aluminum and has a slightly "rougher" texture.
> Could this produce a different way of conducting heat out of the paraffin block than the Shandon?
> Perhaps the stainless steel draws heat from the blocks faster than the aluminum, and thus causes the cracking?
>
> I have used the Shandon Embedding Center for over 24 years.
> I have never had a problem with blocks that crack.
>
> Thanks for any thoughts that you may have on this.
>
> Tim Wheelock
> Harvard Brain Bank
> McLean Hospital
> Belmont, MA
>
>
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