Since Robert Crowningshield's discovery in the late 1950s that diamonds that have been artificially colored by irradiation and subsequent annealing could be identified by their characteristic absorption spectra (in particular, the band at 595 (592) nm), much more information has become available about the radiation-related bands seen in the visible spectra of diamonds. The introduction of cryogenics has made the observation by hand spectroscope or the recording by spectrophotometer of a diamond's visible spectrum less troublesome. But it has also opened the eyes of the gemologist to the fact that virtually any band that can be artificially induced in the spectrum of diamond by irradiation and subsequent annealing can also occur naturally. This makes identification of the source of color in some diamonds, particularly fluorescent green and some yellow stones, very difficult.
