One of the earliest methods used to modify diamond color was?

• A. Coatings.
• B. HPHT treatment.
• C. Irradiation.
• D. Laser drilling.

Answer: (C)

Color modification in diamonds is about changing the internal structure so light interacts differently. Exposing a diamond to high‑energy radiation creates defects, or color centers, in the crystal lattice. These centers absorb certain wavelengths of light, producing a new color—blue or green are common outcomes—and the color can be stabilized by a controlled heating step. This approach directly changes the gemstone’s interior rather than just altering its surface appearance with coatings, making it one of the earliest practical methods used to change diamond color. Coatings are superficial and can wear off; HPHT treatment and laser drilling came later and serve different purposes or are more modern techniques.