Name two common diamond treatments and their general effect.

• A. Coating (adds optical color) and annealing (increases clarity)
• B. Laser drilling (increases hardness) and fracture filling (improves transparency)
• C. HPHT (color modification, often reducing yellow) and irradiation (color change to blue/green/pink)
• D. CVD growth (increases mass) and HPHT (removes inclusions)

Answer: (C)

Diamonds are often treated to change their color, and the most common methods used for this are HPHT and irradiation. High-pressure, high-temperature treatment alters the crystal lattice and impurities, which can reduce a yellow tint and produce colorless or new fancy colors. Irradiation exposes the diamond to energetic particles that create color centers in the lattice, resulting in blue, green, or pink hues; this color is usually stabilized by a subsequent heat treatment. These two approaches are widely used in the industry to achieve noticeable color changes and are typically disclosed to buyers. Other options describe treatments that target surface appearance or clarity, or don’t primarily produce color changes, so they don’t fit as the two standard color-changing methods.