8. Diamond Grading

DIAMOND GRADING: est stim ima ati tion on of the e qu qua ali lity ty and o f th t he valu va lue e of di dia amo mond nds s Univ.Prof.Dr.Corina Ionescu 2011

Universitatea Universita tea “Babes-Boly “Babes-Bolyai” ai” Cluj-Napoca Cluj-Napoca.. Catedra de Mineralogie. Mineralogie. No reproduction, copy or transmission transmission of this file or part of this file may be made without permission of the author. The file is only for internal use in the Chair of Mineralogy, Mineralog y, Babes-Bolyai University of Cluj-Napoca, Cluj-Napoca, Romania.

General data

•Definition: estimation of the quality of diamonds (classification in quality classes) and estimation of the value (price) •Suitable only natural diamonds: » Cut diamonds » Loose stones » Laser -drilled diamonds • No Nott for: » Treated (irradiated, dyed, HTHP) diamonds » Synthetic diamonds » Rough stones » Fracture-filled diamonds

General data

• International Diamond Council rules • 10x loupe • Artificial light

equivalent to day light (3 bulbs each of 8 watt)

General data Main parts of a brilliant-cut diamond

General data • Order of observation: • crown • pavilion • side (girdle)



I. Estimation of the quality classes

The 4 c ’ ’

1. Colour 2. Clarity 3. Cut 4. Carat

1. Colour

Colour grading: 6 classes based on the increasing yellow saturation

EW

RW

W

STW

TW

TC

Colour grading

Colour grading Six Master stones: cubic zirconia (synthetic product): EW, RW, W, STW,

TW, TC

Colour grading GIA (Gemological Institute of America) colour grading scale

Colour grading Sy m b o l s f o r c o l o u r g r ad i n g (G A I A s y s t em )

D E F G H I J K L M

O Z

Co l o u r c l as s es u s ed t i l l 1990

Co l o u r c l as s es (ac t u al s y s t em , Eu r o p e)

Sy m b o l s f o r c o l o u r c l as s es (Eu r o p e)

River

Exceptional white

EW

Top Wesselton

Rare white

Wesselton Top Crystal Crystal

White

RW W

Slightly tinted white

STW

Top Cape

Tinted white

TW

Cape Yellow

Tinted colour (Light yellow) Fancy diamonds (All colours)

TC1

TC4

2. Clarity

Clarity grading

Clarity grading

Clarity grading • Internal features: features inclusions, cracks, structural planes • External features [scratches, polishing lines, pits, cavities, natural faces (remnants), structural lines] which may decrease the clarity

Clarity grading: “inclusions” - inclusions / solid, liquid, gas - cracks - growth lines - twinning planes - cleavage planes

Clarity grading: 7 classes • LC or IF (Loupe clean or Internally flawless) • •

VVS (Very very small inclusions) VS (Very small inclusions)

• SI (Small inclusions) • P1 (Pique 1) • P2 (Pique 2) • P3 (Pique 3)

Clarity grading: LC (Loupe clean) class (or IF - Internally flawless) • Free from any “inclusion” at 10X loupe, nothing to be seen respectively; • In USA no external defects are accepted; • In Europe only external features which do not diminish the clarity, are accepted: small cleavage cracks along the girdle, growth lines, twinning lines.

Clarity grading: LC (Loupe clean) class

Clarity grading: VVS class (Very very small inclusions)

• Very, very small “inclusions”, difficult to be seen with 10X loupe • The nature of the “inclusions” is impossible to be find only with 10X loupe









Clarity grading: VS class (Very small inclusions)

Very small “inclusions”, which are difficult to be seen with 10X loupe






Clarity grading: SI class (Small inclusions)

• Small “inclusions”, easily to be seen with 10X loupe but invisible with naked eye • The presence of “inclusions” do not diminish the brilliance of the diamond









Clarity grading: P1 class (Pique 1) or Imperfect 1 • Inclusions visible by naked eye, easily to be identified with 10X loupe • The inclusions do not diminish the clarity/brilliance of the diamond

Clarity grading: P1 class (Pique 1)





Clarity grading: P2 class (Pique 2) or Imperfect 2 • Numerous and/or larger “inclusions”, easily to be seen with naked eye; • the “inclusions” lightly diminish the clarity/brilliance of the diamond.





Clarity grading: P3 class (Pique 3) or Imperfect 3

• Larger and/or numerous “inclusions” easily seen with naked eye; • The “inclusions” strongly diminish the clarity/brilliance of the diamond.






Clarity grading P3 class (Pique 3)

The 4 c ’ ’

3. Cut

Cut grading A. Proportions B. Symmetry features C. Polishing quality (finishing)


Cut grading: proportions • Table diameter • Crown angle • Pavilion depth

Cut grading: proportions Pr o p o r t i o n s

Med i u m t o p o o r < 53%

53 – 55%

56 – 66%

67 – 70%

Med i u m t o p o o r > 70%

Crown height

< 9%

9 – 10%

11 – 15%

16 – 17%

> 17%

Crown angle

< 27

31 – 37o

38 – 40

Pavilion depth

< 40%

40 – 41%

42 - 45%

46 – 47%

> 47%

Extremely thin

Very thin

Thin to medium (2-

Thick

Very thick

Small to medium (2%)

Large (3-4%) or no culet

Table diameter

Girdle thickness

Culet size

o

Large (3-4%) or no culet

Go o d

27 – 30

Ver y g o o d

o

Small to medium (2%)

4%) Small (1%)

Go o d

o

o

> 40

Cut grading: proportions

Cut grading: proportions

Cut grading: proportions Empiric estimation: table diameter ~ 54%



Cut grading: proportions Empiric estimation: crown angle

Cut grading: proportions Empiric estimation: girdle thickness

Cut grading: proportions Empiric estimation: culet size

No culet

Small culet

Medium culet

Large culet

Very large culet

Cut grading: proportions Empiric estimation: very good brilliance (very good proportions - pavilion of 43-44%)

Cut grading: proportions Empiric estimation: good brilliance (good proportions -pavilion 46%)

Cut grading: proportions Empiric estimation: Medium brilliance (good proportions -pavilion 48%)

Cut grading: proportions Empiric estimation: medium brilliance (medium proportions-pavilion about 48%)

Cut grading: proportions Empiric estimation: poor brilliance (poor proportions - too shallow pavilion, <40%)


Cut grading: symmetry A. Proportionoscope: measurable features - Deviation from a perfect round shape of the girdle (off round) - Table parallel to the girdle plane - Eccentric table or/and culet

Cut grading: symmetry B. 10X loupe: not-measurable features: - Asymmetric table - Asymmetric culet - Facets of unequal size - Unequal thickness of the girdle - Missing the meet-point of the facets edges

Cut grading: symmetry






Cut grading: symmetry Po i n t s (d ed u c t i o n s )

Sy m m et r y

0–3

Very good

3–6

Good

6 – 12

Medium

> 12

Poor


Cut grading: finishingpolishing

Cut grading: finishingpolishing Quality of the sur f fa ce

Polishing quality

Without any polishing lines Few polishing lines

Very good

Numerous and visible polishing lines Polishing lines which diminish the brilliance of the diamond

Good Medium Poor

The 4 c ’ ’

4. Carat

Carat grading • Mass (“weight”): carat 1 ct = 0.215 g 1ct = 100 points • Weighting: balance, scale • Mass (carat) = diameter 2 x total depth x 0.0061 (up to 0.0064)

Carat grading The value: only recalculated mass (measured mass minus the deductions due to the deviation from ideal proportions, symmetry and polishing)

BABEŞ-BOLYAI UNIVERSITY CLUJ-NAPOCA FACULTY OF BIOLOGY AND GEOLOGY GEMOLOGICAL LABORATORY Nr._____________________-

DIAMOND GRADING REPORT Cut style and shape: brilliant, round Dimension_____________________mm Mass (“weight”)__________________ct

PROPORTIONS_________________ Table (%) Crown height(%) Pavilion depth (%)

_____ ___

_________

Red coloured symbols represent internal features. Green coloured symbols represent external features. The symbols indicate the nature and position of the features and not necesarly their size.

__________

Girdle_____________________ Culet______________________

FINISHING______________________ Polishing________________ Symmetry_______________

CLARITY_________________ COLOUR___________________ Visual________________ Photometric_____________ Luminiscence___________

COMENTS

DIAMOND EXPERT Name ________________________ Signature _____________________ Data__________________________

II. Value

Base for evaluation: value of an ideal diamond W-LC: white, loupe clean Mas s (“ w ei g h t ” )

Pr i c e p er c t ( î î n $) – – f o r 1999

0,18 – 0,19 ct 0,30 – 0,32 ct 0,40 – 0,42 ct 0,50 – 0,59 ct 0,70 – 0,74 ct 0,94 – 0,95 ct 0,96 ct 0,97 ct 0,98 ct

900 2.300 2.600 2.800 2.950 3.200 3.300 3.400 3.500

0,99 ct 1,00 ct

3.600 4.000

Ratio (%) between the ideal diamond value and other diamonds LC

VVS

VS

SI

P1

P2

P3

Exceptional white (EW)

170

140

100

70

60

50

35

Rare white (RW)

140

100

90

65

50

40

30

White (W)

100

80

75

60

45

35

25

Slightly tinted white (STW)

80

70

65

55

35

30

20

Tinted whi te (TW)

70

60

45

35

25

20

15

Tinted (TC2)

50

40

30

25

20

15

10

colour

Eureka diamond

Guineea Star diamond

Princesse cut diamond

8. Diamond Grading

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