Two different non-oxide ceramics, Si3N4 and SIC, were characterized with respect to their grain-boundary structure employing both scanning and transmission electron microscopy. The latter method, which enables one to gain direct insight of the atomistic interface structure, was utilized to verify whether grain-boundary wetting occurred. SEM imaging of plasma-etched surfaces revealed a characteristic bright contrast along interfaces for both ceramics, Si3N4 as well as SIC, suggesting the presence of an intergranular glass film. High-resolution TEM studies of the Si3N4 sample confirmed that these fine bright lines along grain boundaries represent intergranular glass films separating Si3N4 matrix grains. However, when high-resolution TEM was employed on SIC samples, which showed a similar contrast variation across SIC grain boundaries In the SEM, the presence of residual glass films was not detected. The SiC materials showed clean grain boundaries with no indication of residual glass even at triple pockets. Chemical analysis monitored yttrium and aluminum segregation at interfaces, which creates a potential barrier (space charges) and therefore affects both the inner mean potential at the interface (Fresnel fringes) and the plasma-etching response. Although SEM imaging showed a similar interface contrast for both Si3N4 and SIC ceramics, HRTEM studies clearly revealed grain-boundary wetting in the former and clean interfaces in the latter material, respectively. Hence, SEM imaging and Fresnel fringe TEM imaging alone are not conclusive when characterizing Interface wetting in ceramic polycrystals.