Grading Proportions-Table, Crown, And Girdle (Chapter 14, Key Terms & Key Concepts) Flashcards
The result achieved by
adding the smallest and largest diameter measurements of a round brilliant and dividing by two.
Average girdle diameter
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 average girdle diameter
Crown height percentage
A weight-retention method where the
cutter leaves more girdle thickness to allow for later
removal of clarity characteristics around the girdle.
Digging out
The width of a fashioned gem’s
girdle.
Girdle thickness
A weight-retention method that adjusts
the angles of some facets to allow portions of a
diamond’s girdle to be thicker.
Painting
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
A transparent measuring device
divided into millimeters and tenths of a millimeter,
used to measure a diamond’s table.
Table gauge
A diamond’s table size expressed
as a percentage of its average girdle diameter.
Table percentage
Table-to-culet depth,
expressed as a percentage of average girdle
diameter
Total depth percentage
Average girdle diameter is the basis for comparing a
diamond’s other proportions.
Key Concept
Diamonds are always measured in millimeters.
Key Concept
Most round brilliants have table percentages that range from
about 55 percent to about 65 percent.
Key Concept
To determine a round brilliant diamond’s table size, measure
the table facet in four directions and average the measurements.
Key Concept
With practice, table-size estimation techniques can be quick
and fairly accurate.
Key Concept
A shallow crown can help a cutter save weight from shallow
rough, but it can have a negative effect on appearance.
Key Concept
A diamond’s girdle should be thick enough to prevent
chipping, but not so thick that it detracts from the stone’s
appearance.
Key Concept
Severe painting and digging out result in hill positions of
differing thicknesses and uneven scalloping around the girdle.
Key Concept
Significant painting or digging out can give a diamond an
unattractive scintillation pattern or make it appear darker.
Key Concept
