RE: [Histonet] Concave wax blocks

From:"Tony Henwood"


The Concave wax blocks problem occurs when there is a little too much xylene left in the wax blocks or if the blocks are insufficiently processed. Check the age of the last wax (how many blocks have been processed) or you might need to increase the time of processing. Is the vacuum still working?

What seems to happen is that as the wax block dries, xylene &/or alcohol evaporates causing concavity of the blocks.
To fix it you will need to melt the blocks and re-embed them in fresh wax (to obtain quick sections). For long term correction, leave the blocks in molten wax to fully remove any trace solvents and re-embed.


Tony Henwood JP, MSc, BAppSc, GradDipSysAnalys, CT(ASC)
Laboratory Manager & Senior Scientist
The Children's Hospital at Westmead,
Locked Bag 4001, Westmead, 2145, AUSTRALIA.
Tel: 612 9845 3306
Fax: 612 9845 3318

-----Original Message-----
From: [] On Behalf Of Timo Väisänen
Sent: Monday, 5 June 2006 11:54 PM
Subject: [Histonet] (no subject)

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 Väisänen PhD 
Oulu University Hospital
Department of Pathology

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