CDG Diamond Grading & Evaluation Techniques 3 — Questions and Answers
Question 1: When color grading a diamond, the stone should be placed in which orientation relative to the master comparison stones?
- Table-up, face view
- Pavilion-up, matching the comparison stone orientation (Correct answer)
- Girdle-view only
- Culet-down
Correct answer: Pavilion-up, matching the comparison stone orientation
Diamonds are graded color with the pavilion facing up (table down) in a folded grading trough, matching the orientation of master comparison stones.
Question 2: What is the purpose of using master comparison stones in color grading?
- To measure the diamond's refractive index
- To provide calibrated color benchmarks for comparison (Correct answer)
- To check the diamond's fluorescence level
- To verify the diamond's weight
Correct answer: To provide calibrated color benchmarks for comparison
Master comparison stones are GIA-graded diamonds used as color benchmarks to ensure consistent and accurate color grade assignments.
Question 3: Under which lighting condition should color grading of a diamond be performed for consistency?
- Direct sunlight
- Fluorescent daylight-equivalent lighting (D65) (Correct answer)
- Incandescent lamp at 60W
- UV blacklight
Correct answer: Fluorescent daylight-equivalent lighting (D65)
Color grading is performed under controlled daylight-equivalent fluorescent lighting (approximately 6500K color temperature) to prevent distortion of body color.
Question 4: A diamond with a GIA color grade of 'D' is described as:
- Faint yellow
- Colorless, the highest color grade (Correct answer)
- Near colorless
- Very light yellow
Correct answer: Colorless, the highest color grade
D is the highest color grade on the GIA scale, representing a perfectly colorless diamond with no detectable hue.
Question 5: Which characteristic most commonly causes a grader to assign a lower (more yellow) color grade to a diamond?
- High fluorescence under UV
- Presence of nitrogen atoms in the crystal lattice (Correct answer)
- Extensive surface scratches
- A high depth percentage
Correct answer: Presence of nitrogen atoms in the crystal lattice
Nitrogen atoms incorporated into the diamond's crystal lattice absorb blue light, causing the stone to appear yellowish, which lowers its color grade.
Question 6: When grading color, a grader should avoid wearing which of the following to prevent bias?
- Disposable gloves
- Brightly colored clothing that reflects onto the stone (Correct answer)
- A magnifying loupe
- A clean white grading trough
Correct answer: Brightly colored clothing that reflects onto the stone
Brightly colored clothing or jewelry can reflect color onto the diamond and influence the grader's perception of the stone's body color.
Question 7: On the GIA color grading scale, the 'near colorless' range encompasses which letter grades?
- D–F
- G–J (Correct answer)
- K–M
- N–R
Correct answer: G–J
Grades G through J are classified as 'Near Colorless,' showing traces of color detectable only by a trained grader under controlled conditions.
CDG Diamond Grading & Evaluation Techniques 3
When color grading a diamond, the stone should be placed in which orientation relative to the master comparison stones?