I store all my IHC tissue blocks in the freezer. I cut controls fresh each
time along w/ the patient tissue. I do this because staining intensity could
differ if I store precut slides. I will freeze slides and controls, however,
if I need to stain on Monday AM and I can cut them Sat. Then they get the
exact same treatment for both the control and unknown slides. My source is
Patrick C. Roche Ph.D. from an old article in CAP Today. I could fax you the
info if you really want. 

Bruce Gapinski HT(ASCP)