I have a glycerol based formula for storage of frozen sections (post acetone/methanol fixed). Entire racks of slides were immersed in the glycerol then stored -20. The glycerol doesn't freeze, but prevents ice crystals. It was easy to retrieve selected slides while the others remained at -20. I used this for ER/PgR tumor control sections which retained antigenicity for (minimally) two years. If anyone is interested, I'd be happy to forward the recipe.
Jacqueline M. O'Connor HT(ASCP)
Global Pharmaceutical Research and Development