Cracks in Paraffin Wax Blocks


Dear All,

Please could anybody tell me why I am getting cracks in my paraffin wax 
blocks?  I noticed someone had asked this question a couple of years ago 
but there was no reply posted.  I can still cut sections from these blocks 
and they look fine under the microscope.  Not all the blocks in a batch are 
cracked, some are nice and I've even had batches where 90% of the blocks 
are good and only a few have cracks.

We use Surgipath Formula R paraffin wax and I have spoken to the rep there 
and he suggested a couple of things, but none have made any difference; he 
has also checked the batch of wax we were using and there are no reported 
problems; besides we are now onto another batch and the same thing happens. 
 I have wondered whether it is my embedding technique, but have tried many 
different ways, e.g. different amounts of wax in the base mould before 
orientation, different lengths of time on the refrigeration spot before 
topping up and different methods of cooling, ie. using the coldplate and 
-20 freezer.  I am also careful not to move the tissue once the wax starts 
to solidify.  The wax is melted at 60 degrees celsius in the processor and 
the embedding centre is also set at 60.

I would be very grateful if anyone has anyone got any suggestions?

Thanking you in advance.

Nicola Cragg
Epistem Ltd.
Manchester, UK

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