What can affect the color resulting from irradiation?

• A. The cut grade of the diamond.
• B. The isotopic composition of carbon.
• C. The defects already present in the diamond.
• D. The geographic origin.

Answer: (C)

Color from irradiation comes from color centers formed in the diamond’s lattice when energy is deposited, creating vacancies and other defects. What color centers end up forming, and how stable they are, depends on the diamond’s pre-existing defects and impurities. If a diamond already contains nitrogen impurities or specific defect clusters, the irradiation-created vacancies interact with those impurities in particular ways, producing different color centers and thus different colors than a diamond with a very clean lattice would produce. In short, the pre-existing defect landscape of the crystal shapes which color centers develop and how they express color after irradiation (including any changes during subsequent heating).

The other factors listed don’t govern this process: the cut grade affects light performance but not the physics of defect formation; the isotopic composition of carbon has negligible influence on irradiation-induced color; geographic origin doesn’t alter the defect chemistry that governs color centers.