A review of the “foundation” of GIA’s new cut grade system

RD19 HCA 7.5 (Fish eye)

RD33 HCA 10? (off scale)

RD37 HCA 6.5 (Fish eye)

Ideal-Scope Lighting

Jewellery Shop Lighting

Disco Lighting

GIA photo 0.72ct

GIA photo 0.64ct

GIA photo 0.50ct

DiamCalc Scores

Light Return Mono

0.97

Light Return Mono

0.79

Light Return Mono

0.93

Light Return Stereo

0.95

Light Return Stereo

0.82

Light Return Stereo

0.94

Contrast

0.83

Contrast

1.00

Contrast

0.92

Specifications

Specifications

Table Size

62% 63

Table Size

56%

Table Size

70%

Crown Angle

29.0° 29.2

Crown Angle

37.0°

Crown Angle

33.5°

Pavilion Angle

39.6° 39.5

Pavilion Angle

44.0°

Pavilion Angle

40.2°

Star Length

50% 51.7

Star Length

55%

Star Length

60%

Lower Girdle

75% 76

Lower Girdle

70%

Lower Girdle

80%

Girdle Thickness

Med 3.3

Girdle Thickness

Thn-Med

Girdle

Stk-Thk Bruted

Culet Size

None

Culet Size

None

Culet Size

None

Total Depth

54.5%

Total Depth

68.0%

Total Depth

56.9%

Polish

Symmetry

COMMENTS: The second stone is so bad it is hard to imagine the need for a lower grade?

This stone will show a fish eye and has very poor contrast. Its light return is very good because it has very little leakage, but its pattern is unattractive. The combination of shallow crown and pavilion angles increases the likelihood of chipping at the girdle.

This diamond will appear to be very much smaller than you would expect for its weight. This is not just because of its smaller diameter – but more so because of the upper girdle leakage. The table is dull because it acts like a mirror, reflecting back in the same direction – it is a nail head.

Described as a slight fish eye with “general darkness”, its main problem is a lack of contrast and scintillation aided by a pronounced inclusion like fish eye. Light return should be quite good.

Had the LG’s been shorter by just 1% or 2%, fatter dark main facets would add contrast. Spread is just OK.