GIA Diamond Proportions & Cut Analysis

Question 1

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

Accepted Answer

The ratio of the table facet width to the average girdle diameter

Answer

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?

Accepted Answer

The angle between the pavilion main facets and the girdle plane

Answer

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?

Accepted Answer

Total depth (table to culet) divided by the average girdle diameter, multiplied by 100

Answer

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?

Accepted Answer

54–57%

Answer

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?

Accepted Answer

The width of the band separating the crown from the pavilion

Answer

Girdle thickness describes the width of the narrow band separating the crown from the pavilion, typically graded from Extremely Thin to Extremely Thick.

(GIA) Certified Diamonds Gemological Institute of America Practice Test

(GIA) Certified Diamonds Gemological Institute of America Practice Test

GIA Diamond Proportions & Cut Analysis