Timo: 
  Which is your processing protocol? How frequently do you change your reagents?
  I have been told that in your country xylene is being susbtituted by isopropanol. Are you using a xylene substitute?
  It seems that the tissues are reaching the paraffin with a large "carry over" from the previous reagents and the problem you describe was quite frequent in the past when aniline oil and benzene were carried over. On such cases the paraffin around the tissue not only contracted but became darker and softer.
  Try to check the changing schedule on your reagents; probably that will be the cause.
  Hope this will help you.
  René J.

Timo Väisänen  wrote:
  Dear all,

Has anyone encountered the following problem? The surface of newly embedded
paraffin blocks start to become concave only after few days. This is not a
problem with normal tissue specimens but with for example small biopsies the
uneveness creates difficulties. Biopsies on the edge of the block run out if
you try to trim the block enough to get the samples in the middle of the block
to the same section with the other samples. I quess paraffin can contract but I
have always thought that this takes years. Could there be something wrong with
the paraffin? Any suggestions? 
Thank's in advance,

Timo 

Timo Väisänen PhD 
Oulu University Hospital
Department of Pathology
Finland









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