What colors can irradiation and annealing produce in a type Ia diamond?

• A. Pink bodycolor.
• B. Yellow, orangy yellow, yellow-green, or brown bodycolor.
• C. Blue bodycolor.
• D. Colorless.

Answer: (B)

When nitrogen is present in aggregated forms in type Ia diamonds, irradiation creates lattice damage (vacancies) and, upon annealing, these vacancies migrate and pair with nitrogen to form color centers. These centers absorb certain wavelengths of light, typically producing yellow to brown hues. The specific hues—yellow, orangy yellow, yellow-green, or brown—depend on the exact defect configurations and the irradiation/annealing conditions. Blue colors come from boron-related centers (not the nitrogen aggregates in type Ia), pink involves other rare distortions, and colorless would require the absence of the color centers created by this treatment. So irradiation and annealing in a type Ia diamond most commonly yield yellow to brown bodycolors.