Diamond Proportions & Cut Analysis Flashcards

What does 'table percentage' refer to in diamond proportions?

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.

In a round brilliant diamond, what does the pavilion angle measure?

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.

How is 'total depth percentage' calculated in diamond grading?

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.

Which table percentage range is generally associated with a GIA Excellent cut grade for a round brilliant diamond?

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.

What does 'girdle thickness' describe in the context of diamond grading?

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.

What is the 'culet' in diamond anatomy?

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.

What are the five cut grades GIA assigns to round brilliant diamonds?

Answer: Excellent, Very Good, Good, Fair, Poor

GIA assigns five cut grades for round brilliant diamonds: Excellent, Very Good, Good, Fair, and Poor.