A vacuum-tight transfer stage is described, that enables air or moisture sensitive specimens to be safely transferred from a protective environment, like that in a dry box, to a scanning electron microscope without exposing the sample to ambient conditions. The transfer stage concept described here is, in fact, applicable to the protected transfer of hygroscopic or air-sensitive samples to any vacuum-based analysis equipment where the transfer device opens automatically under vacuum to reveal the sample. This device concept is also applicable to the transfer of samples under vacuum from one glove box to another where the transfer chamber can be easily opened manually to reveal the sample. An example of one application of the device is provided by a controlled exposure study of stabilized lithium metal particles (SLMP) at various stages of shelf life. We found that a reaction coating formed on "fresh" SLMP after it was exposed to 100 Pa air for as short as 15 m. Such a reaction to air exposure was not observed on "aged" SLMP with a thickened carbonate surface coating after 4 and 6 months of shelf life. The case study of the surface coating on SLMP clearly demonstrated the excellent vacuum performance of the novel transfer stage.