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)
General data • Order of observation: • crown • pavilion • side (girdle)
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: VVS class (Very very small inclusions)
Clarity grading: VVS class (Very very small inclusions)
Clarity grading: VVS class (Very very small inclusions)
Clarity grading: VVS class (Very very small inclusions)
Clarity grading: VVS class (Very very small inclusions)
Clarity grading: VVS class (Very very small inclusions)
Clarity grading: VVS class (Very very small inclusions)
Clarity grading: VVS class (Very very small inclusions)
Clarity grading: VS class (Very small inclusions)
Very small “inclusions”, which are difficult to be seen with 10X loupe
Clarity grading: VS class (Very small inclusions)
Clarity grading: VS class (Very small inclusions)
Clarity grading: VS class (Very small inclusions)
Clarity grading: VS class (Very small inclusions)
Clarity grading: VS class (Very small inclusions)
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: SI class (Small inclusions)
Clarity grading: SI class (Small inclusions)
Clarity grading: SI class (Small inclusions)
Clarity grading: SI class (Small inclusions)
Clarity grading: SI class (Small inclusions)
Clarity grading: SI class (Small inclusions)
Clarity grading: SI class (Small inclusions)
Clarity grading: SI class (Small inclusions)
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: P1 class (Pique 1)
Clarity grading: P1 class (Pique 1)
Clarity grading: P1 class (Pique 1)
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: P2 class (Pique 2)
Clarity grading: P2 class (Pique 2)
Clarity grading: P2 class (Pique 2)
Clarity grading: P2 class (Pique 2)
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)
Clarity grading: P3 class (Pique 3)
Clarity grading: P3 class (Pique 3)
Clarity grading: P3 class (Pique 3)
Clarity grading: P3 class (Pique 3)
Clarity grading P3 class (Pique 3)
The 4 c ’ ’
3. Cut
Cut grading A. Proportions B. Symmetry features C. Polishing quality (finishing)
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: table diameter ~ 60%
Cut grading: proportions Empiric estimation: table diameter ~ 66%
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 A. Proportions B. Symmetry features C. Polishing quality (finishing)
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
Cut grading: symmetry
Cut grading: symmetry
Cut grading: symmetry
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 A. Proportions B. Symmetry features C. Polishing quality (finishing)
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