A method of non-destructive detection of solid inclusions with varying sensitivities but highly congruent positional identification by both short-wavelength and long-wavelength methods. The short-wavelength method consists of lateral scatter (LS) and the long-wavelength method consists of THz imaging. The LS method was able to detect all agglomerated inclusions, transparency variations, voids, and localized phase differences. The THz imaging was able to routinely detect solid inclusions and index inhomogeneity. In combination, the LS and THz imaging methods were able to detect all relevant types of material variation, so that the combination of the two non-destructive testing methods provides a solution capable of detecting the full array of critical material variations in transparent polycrystalline ceramic materials.