This is due to the cold plate being too cold. I once had a loaner embedding center while my own embedding center was being repaired, and I had the same problem.  The cold plate on that unit was -8 degrees C, while the cold plate on my own unit was 0 degrees C. I found that the blocks would separate from the molds in much less time then they would on my own unit. In fact, the blocks would come loose from the molds while the top of the paraffin block still felt fairly warm to the touch.  If you left the blocks on the cold plate until the tops of the blocks felt cold, you would find cracks in the cutting surface of the block.  I did find however that these cracks were often just on the surface, and that in facing off the blocks I would get in past the cracks. Even when some cracks remained, they did not seriously affect sectioning of the blocks.  But the cracks could be avoided by removing the blocks from the cold plate after a short period of time.  If I had to continue using that unit I would have looked into having the cold plate temperature reduced, but since I only had it a couple of weeks, I just worked around the problem.

> ----------
> From: 	histonet-bounces@lists.utsouthwestern.edu on behalf of Bales, Candy A
> Sent: 	Tuesday, May 22, 2007 3:46 PM
> To: 	histonet@lists.utsouthwestern.edu
> Subject: 	[Histonet] cracks in paraffin
> 
> Greetings. I am writing on behalf of a friend who is in need of
> assistance.
>  
> Since purchasing a new embedding center, she has noticed that her
> paraffin blocks are cracked when she removes them from the molds. She
> has checked her temperatures on the embedding machine. She has not
> changed paraffin brands/types. She uses paraplast plus.
>  
> She has tried spraying the molds. 
>  
> Any suggestions would be appreciated.
>  
> Thank you
>  
> C. Bales, H.T.
> University of Texas Dental Branch
> Houston, TX
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> Histonet@lists.utsouthwestern.edu
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> 
> 
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