The High Resolution Camera, or HRC, is a set of microchannel plate based detectors designed to fly aboard the Advanced X-Ray Astrophysics Facility (AXAF), one of the "Great Observatories" under the auspices of NASA. The HRC is designed in two configurations, one for direct imaging and the other for reading out the spectrum of transmission gratings for high resolution spectroscopy. The current design calls for different photocathodes: the imaging detector will have a CsI coating, and the spectroscopic detector will have KBr. Since the instrument is expected to perform over an extended period in space, we are interested in the long-term behavior of these coatings in vacuum. In this paper, we examine the current ROSAT experience from flight calibration observations with the HRI (the predecessor of HRC), and we outline plans for a test of the long-term stability of these coatings in vacuum and under nitrogen storage.