Assignment 12/13 - Grading Proportions Flashcards
The result achieved by adding the smallest and largest diameter measurement of a round brilliant and dividing by two.
Average girdle diameter.
Table-to-culet depth, expressed as percentage of the average girdle diameter
Total depth percentage
How does average girdle diameter relate to other proportions?
Average girdle diameter is the basis for comparing a diamond’s other proportions.
How do you determine total depth percentage?
divide the total depth by the average girdle diameter.
How can you recognize overweight diamonds?
Generally a total depth percentage of >65%.
A diamond’s table size expressed as a percentage of its average girdle diameter
Table percentage
How do variations in a diamond’s table size affect its appearance?
A too large or too small table have a negative impact on brightness and fire. Most brilliants have a table percentage between 55% and 65%.
What are the methods for determining table size
- Direct Table Measurement (Table gauge & loupe)
- Estimating (Flash, Ratio or Bowing method)
A transparent measuring device divided into millimetres and tenth or a millimetre, used to measure a diamond’s table
Table gauge
The length of the star facets expressed as a percentage of the total distance between the girdle and the edge of the table facet.
Star length percentage
How do star facets affect a diamond’s appearance
They mainly affect a diamonds symmetry.
The angle formed by the bezel facets and the girdle plane.
Crown Angle
The distance from the girdle plane to the table, expressed as a percentage of the average girdle parameter.
Crown Height Percentage
What are the effects of a shallow and steep crown angle?
The have a negative effect on brightness and fire.
What techniques can you use to estimate crown angles?
- Profile Method
- Faceup Method
How does the girdle thickness affect a diamond’s durability and appearance ?
A girdle should be thick enough to prevent chipping but not so thick that it detracts from the stone’s appearance.
How doe you estimate girdle thickness?
Assess at 10x:
Extremely thing (ETN) - knife-edge
Very Thin (VTN) - very thin line
Thin (THN) - a thin line
Medium (MED) - distinct line
Slightly thick (STK) - obvious
Thick (THK) very obvious
Very thick (VTK): distracting
Extremly Thick (ETK): very distracting
A weight-retention method that adjust the angles of some facets to allow portions of a diamonds girdle to be thicker.
Painting
A weight-retention method where the cutter leaves more girdle thickness to allow for later removal of clarity characteristics around the girdle
Digging out
Where is the focus when describing girdle thickness?
Valleys
What facets are used to estimate the crown angle in profile?
Table and bezel facets
The quality of the polish and precision of the cut of fashioned gemstones
Finish
How do variations in pavilion dimensions affect a diamond’s appearance?
The pavilion makes a significant contribution to brightness and fire.
How are pavilion depth percentage and pavilion angle related?
The greater the pavilion depth percentage, the steeper (greater) the pavilion angle.
