CDG Case Analysis & Practical Application 3 — Questions and Answers
Question 1: A round brilliant diamond has a table percentage of 72% and a crown angle of 25 degrees. How does this combination most likely affect light performance?
- It produces maximum fire and brilliance
- The large table combined with a flat crown reduces fire and may create a 'fisheye' effect (Correct answer)
- Crown angle has no effect when the table is over 70%
- This combination is ideal for step-cut diamonds only
Correct answer: The large table combined with a flat crown reduces fire and may create a 'fisheye' effect
A very large table percentage combined with a shallow crown angle reduces the crown's ability to disperse light, diminishing fire and risking a fisheye reflection of the girdle.
Question 2: A diamond grader measures a pavilion angle of 41.5 degrees. What light performance issue is most associated with this steep pavilion?
- Increased light leakage through the pavilion
- A dark 'nail head' appearance in the center of the stone face-up (Correct answer)
- Improved scintillation with no drawbacks
- Higher dispersion leading to excessive fire
Correct answer: A dark 'nail head' appearance in the center of the stone face-up
A pavilion angle above approximately 41 degrees causes light to reflect back at a steep angle, creating a dark central zone known as a 'nail head' effect when viewed face-up.
Question 3: A grader assigning a Polish grade observes minor abrasions on several facet edges but no scratches or nicks. What Polish grade is most appropriate?
- Excellent
- Very Good
- Good (Correct answer)
- Fair
Correct answer: Good
Minor abrasions visible under 10x but not individually severe typically place the polish grade at Good rather than Very Good or Excellent.
Question 4: When assigning a Symmetry grade, you discover the culet is noticeably off-center from the table. Which symmetry grade is most appropriate if this is the only deviation observed?
- Excellent, because only one deviation is present
- Good or Fair, because an off-center culet is a significant symmetry deviation (Correct answer)
- Very Good, as culet placement is not considered in symmetry grading
- Poor, because all off-center culets automatically receive the lowest grade
Correct answer: Good or Fair, because an off-center culet is a significant symmetry deviation
An off-center culet is a significant symmetry characteristic that, even alone, typically lowers the symmetry grade to Good or Fair depending on severity.
Question 5: A cutter has produced a round brilliant with a 34-degree crown angle and a 40.75-degree pavilion angle. How would GIA most likely grade the overall cut?
- Fair, because 34 degrees is too steep for the crown
- Excellent or Very Good, as this combination falls within the optimal range for light performance (Correct answer)
- Good, because any crown angle above 33 degrees lowers the cut grade
- Poor, because pavilion angles below 41 degrees cause light leakage
Correct answer: Excellent or Very Good, as this combination falls within the optimal range for light performance
A crown angle of 34 degrees paired with a pavilion angle of 40.75 degrees falls within GIA's well-documented optimal range for achieving Excellent to Very Good cut grades.
Question 6: You are grading a round brilliant with a girdle that grades as Thick to Very Thick. What is the most significant concern this raises beyond the girdle grade itself?
- Girdle thickness has no impact on any other grade
- The extra weight in the girdle increases carat weight without contributing to face-up size, reducing value per carat (Correct answer)
- A very thick girdle automatically lowers the clarity grade
- Very thick girdles are preferred because they protect the diamond from chipping
Correct answer: The extra weight in the girdle increases carat weight without contributing to face-up size, reducing value per carat
A very thick girdle hides excess weight that does not contribute to face-up diameter, meaning the stone appears smaller than its carat weight would suggest, reducing value per carat.
Question 7: A diamond has 65 facets instead of the standard 58 due to extra facets on the pavilion. How do extra facets affect the GIA cut grade?
- Extra facets always improve the cut grade by increasing scintillation
- Extra facets are noted as a symmetry characteristic and can lower the symmetry grade if they are asymmetrical (Correct answer)
- Extra facets are only noted if there are more than 10 additional facets
- Extra facets are treated as inclusions and affect the clarity grade
Correct answer: Extra facets are noted as a symmetry characteristic and can lower the symmetry grade if they are asymmetrical
Extra facets are a symmetry characteristic; if they are asymmetrically placed or visually disruptive, they are noted on the report and may lower the symmetry grade.
CDG Case Analysis & Practical Application 3
A round brilliant diamond has a table percentage of 72% and a crown angle of 25 degrees.
How does this combination most likely affect light performance?