>>> Sharron Ladd  12/04/02 11:30AM >>>
Are you using metal molds? I learned in a NSH workshop, that leaving
the 
blocks chilling too long on the cold plate (in metal molds) can cause 
cracks to form in the paraffin.
Sharron

ncragg wrote:

>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
>
>Is someone spraying the blocks with     freeze spray to get them cold
faster? That will make cracks.
>
>
>  
>