GIA Diamond Proportions & Cut Analysis 1 — Questions and Answers
Question 1: What does 'table percentage' refer to in diamond proportions?
- The ratio of the table facet width to the average girdle diameter (Correct answer)
- The ratio of the crown height to the total depth
- The number of facets on the table surface
- The percentage of the diamond's volume above the girdle
Correct answer: The ratio of the table facet width to the average girdle diameter
Table percentage is calculated by dividing the table facet width by the average girdle diameter and multiplying by 100.
Question 2: In a round brilliant diamond, what does the pavilion angle measure?
- The angle of the crown facets relative to the table
- The angle between the pavilion main facets and the girdle plane (Correct answer)
- The angle between the star facets and the table
- The angle of the culet relative to the pavilion base
Correct answer: The angle between the pavilion main facets and the girdle plane
The pavilion angle is measured between the pavilion main facets and the girdle plane, and it critically determines how light reflects internally before returning to the viewer's eye.
Question 3: How is 'total depth percentage' calculated in diamond grading?
- Pavilion depth divided by crown height, multiplied by 100
- Total depth (table to culet) divided by the average girdle diameter, multiplied by 100 (Correct answer)
- Crown height divided by the average girdle diameter, multiplied by 100
- Total depth divided by the table diameter, multiplied by 100
Correct answer: Total depth (table to culet) divided by the average girdle diameter, multiplied by 100
Total depth percentage is the total depth (from table to culet) divided by the average girdle diameter, multiplied by 100.
Question 4: Which table percentage range is generally associated with a GIA Excellent cut grade for a round brilliant diamond?
- 45–52%
- 53–58%
- 54–57% (Correct answer)
- 60–65%
Correct answer: 54–57%
GIA research indicates that table percentages of approximately 54–57% tend to fall within the Excellent cut grade range for round brilliant diamonds.
Question 5: What does 'girdle thickness' describe in the context of diamond grading?
- The total weight of the girdle region in carats
- The width of the band separating the crown from the pavilion (Correct answer)
- The number of facets polished along the girdle
- The percentage of the diamond's total depth occupied by the girdle
Correct answer: The width of the band separating the crown from the pavilion
Girdle thickness describes the width of the narrow band separating the crown from the pavilion, typically graded from Extremely Thin to Extremely Thick.
Question 6: What is the 'culet' in diamond anatomy?
- The large flat facet at the top of the diamond
- The small facet or pointed tip at the very bottom of the pavilion (Correct answer)
- A type of clarity inclusion found at the base of the diamond
- The outermost edge of the girdle
Correct answer: The small facet or pointed tip at the very bottom of the pavilion
The culet is the small facet or point at the very bottom of the pavilion; in older diamonds it may be a larger facet visible through the table.
Question 7: What are the five cut grades GIA assigns to round brilliant diamonds?
- Perfect, Excellent, Very Good, Good, Fair
- Excellent, Very Good, Good, Fair, Poor (Correct answer)
- Ideal, Premium, Very Good, Good, Poor
- Excellent, Good, Average, Below Average, Poor
Correct answer: Excellent, Very Good, Good, Fair, Poor
GIA assigns five cut grades for round brilliant diamonds: Excellent, Very Good, Good, Fair, and Poor.
GIA Diamond Proportions & Cut Analysis 1
What does 'table percentage' refer to in diamond proportions?