[Histonet] Tissue separating from the wax when floating out

[Carl Hobbs]

A colleague has brought his pwax blocks of brain tissue from his lab and is 
using my pwax section cutting system to cut his blocks: after floating them 
out on the waterbath ( fresh distilled water, maintained at 40C- yes, we've 
tried lower temps and the sections either just don't flatten out or still 
separate, after a longer period), they separate away from the wax, initially 
along the line of the meninges separating the two areas of brain, in coronal 
section.
I have looked at his blocks and they seem well-processed - no 
fracturing/white areas, a good way to tell is to look at the cut blocks a 
week after sectioning to see if the face of the tissue has shrunk down into 
the block, no they haven't.
I have cut some myself: same problem.
I took one of these blocks and re-immersed it in fresh molten wax for 2hrs 
( I tried simple paraffin wax and then Paraplast Plus)....no improvement.
The blocks serial-section beautifully.
He has asked his lab if they have this problem and they do not. He has not 
seen it before, either, when cutting in his own lab.

This happens to me also, with the occassional block. Has anyone come across 
this problem?
Why does it occur?
( my processing details: 2hrs in each of 30, 70, 95, 100, 100% IMS, 
IMS:Xylene 1:1, xylene, xylene, wax, wax...then 1hr in embedding station wax 
bath. On a Leica processing machine, with agitation.
Embedding is swiftly carried out, so minimal cooling of wax.
Be most grateful for any reasoning.
Best wishes
carl