Re: [Histonet] Concave paraffin blocks

From:"Joe Nocito"

I understand the reasoning behind using the 6 chamber blocks. It's like when 
contractors place steel bars when they pour concrete, it reinforces the 
concrete. However, I don't think this would have any effect on the cutting 
surface of the block.
    I'm not familiar with Histowax so I can not intelligently say it is the 
embedding medium or not. How long has this problem been happening? Have you 
changed anything in the processing of your blocks before this problem 
    I'm sorry I did not see your first posting. Have you tried a different 
paraffin? Can you get some samples from your supplier? If you can't, please 
email me. I'll see what I can do.

Histology Manager
Pathology Reference Lab
San Antonio, TX

----- Original Message ----- 
From: "Timo Väisänen" 
Sent: Tuesday, July 04, 2006 10:22 AM
Subject: [Histonet] Concave paraffin blocks

> Dear all,
> I mailed a while ago a question about concave paraffin blocks and received 
> ample
> of suggestions. Thank you all. Based on them the culprit for our problem 
> was
> suggested to be the excess of xylene in the blocks.
> I have now checked the tissue processors for faulty valves causing 
> carry-over
> etc. and they seemed to be fine. Concave blocks were also present when
> processing was performed with totally fresh paraffin. Therefore, I think,
> carry-over of solvents may not be the cause in our case. Somebody also
> suggested that too low temperature of the cold plate during embedding or 
> when
> cooling the blocks before sectioning could cause the concave surface. I=20
> tested
> this by adjusting the plate temperatures to -5-10C range. This did not 
> help.
> The only thing that seemed to have some kind of positive effect was using 
> six
> chamber biopsy cassettes during the embedding. The rationale in this 
> experiment
> was, that maybe during embedding and when paraffin solidifies the shape of 
> the
> cassette base changes a littel bit and causes tension to the solid 
> paraffin.
> This tension could then cause the concave shape of the block surface. The 
> extra
> plastic in the six chamber biopsy cassette base could make it more rigid 
> and
> resistant to tension/distortion. To my surprise using these cassette bases 
> made
> the blocks more even. Does this theory make any sense? One other thing 
> that came
> to my mind is paraffin itself. We routinely use Histowax 52-54C. Maybe I 
> should
> try another brand?
> Thank you for your comments in advance!
> Timo
> Univ. Hospital of Oulu
> Dept. of Pathology
> Finland
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