Wrinkled, folded, buckled or warped sections can be vacuum dried as follows: a vacuum desiccator is furnished with a layer of calcium sulfate, and with a petri dish filled to a depth of 3 mm with phosphorous pentoxide. A large filter paper (Whatman #1) secured under the tray of the desiccator prevents dust from contaminating slides during pumping. Slides, positioned on top of the tray, are kept in vacuum for 48 hours. Immediately after removal from the vacuum jar, and without immersion in any organic solvent, the slides are coverslipped with mounting media.
Hildegard H. Crowley and Ben H. Leightling (1989). Elimination or Reduction of Wrinkles in Semithin Epoxy Sections by Vacuum Drying. Stain Technology, Vol. 64, No 5, pg. 221-223