If you are working with THICK, ground or ultramilled sections i.e. more
than 7 um or so, cracking will occur.  PMMA removal is designed to be used
on THIN sections, 3 to 7 um or so, so one can do routine staining or
immunostaining where total removal of hydrophobic plastic is required. 

Thick sections are better stained using a surface staining methods.  If you
try an coverslip a thick section with xylene based mounting media, cracking
will also happen. The plastic can be etched with xylene to soften the
plastic, alcohol can also be used so stain penetrates into a few um of the
tissue involved.  OR you can etch with 1% formic acid (surface
decalcification) only a few um so stains i.e. toluidine blue, MacNeals, or
any other penetrate into surface of bone (not soft tissue cells)

There are only a few dyes that penetrate well through PMMA, even with
surface staining and they have very low molecular weights t blue, methylene
blue, basic fuchsin, etc.  There have been publications on this and also
discussed on Histonet before, try the Archives. 


Gayle Callis
MT,HT,HTL(ASCP)
Research Histopathology Supervisor
Veterinary Molecular Biology - Marsh Lab
Montana State University - Bozeman
S. 19th and Lincoln St
Bozeman MT 59717-3610

406 994-6367 (lab with voice mail)
406 994-4303 (FAX)

email: gcallis@montana.edu