Criteria for distinguishing emerald filling substances were investigated. Thirty-nine fillers were divided into six substance categories—three “presumed natural” (essential oils [including cedarwood oil], other oils, waxes) and three “artificial resin” (epoxy prepolymers, other prepolymers [including UV-setting adhesives], polymers). Regardless of their composition, fillers with R.I.’s of 1.54 or above show flash effects in emeralds. On the basis of Raman and infrared spectroscopy, the fillers could be separated into five spectral groups, A through E. Most, but not all, commonly used artificial resins have spectra distinct from that of cedarwood oil. However, the detection of one substance in a fissure does not imply that all others are absent.