Diamond type
Diamond type is a method of scientifically classifying diamonds by the level and type of their chemical impurities. Diamonds are separated into four types: Type Ia, Type Ib, Type IIa, and Type IIb. The impurities measured are at the atomic level within the crystal lattice of carbon atoms and so, unlike inclusions, require an infrared spectrometer to detect.
Diamond simulant
Most "colorless" diamonds are actually tinted yellow or brown to some degree, whereas some artificial simulants are completely colorless—the equivalent of a perfect "D" in diamond color terminology. This "too good to be true" factor is important to consider; colored diamond simulants meant to imitate fancy diamonds are more difficult to spot in this regard, but the simulants' colors rarely approximate. In most diamonds (even colorless ones) a characteristic absorption spectrum can be seen (by a direct-vision spectroscope), consisting of a fine line at 415 nm. The dopants used to impart color in artificial simulants may be detectable as a complex rare-earth absorption spectrum, which is never seen in diamond.