36th international gemmological conference | august 2019 … · an apparent contradiction: “the...
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| PAGE 1
36th International Gemmological Conference | August 2019
| STUDY OF A RECUT HPHT SYNTHETIC DIAMOND:
COLOUR VS SIZE VS SWUV TRANSMISSION
Presentation by J-P. Chalain
| PAGE 2
| STUDY OF A RECUT HPHT SYNTHETIC DIAMOND C O L O U R V S S I Z E V S S W U V T R A N S M I S S I O N
• Context & Challenges
• Recut of a HPHT synthetic diamond
• Colour vs Size
• SWUV transmission vs Size
• Normalized SWUV transmission vs Colour
• Conclusion
LAYOUT
| PAGE 3
| CONTEXT & CHALLENGES
Automated Spectral Diamond Inspection - ASDI
ASDI • 1st automated machine for separating natural D to J melees from possible synthetics • Rejects all colourless diamonds transparent to SW (270 nm) • So far, N-doped CVD synthetic diamonds are not in the “D - J colour range.”
DPA Project Assure • 2019: ASDI passed 100% of the DPA-Project Assure Tests • Testing samples: 1’000 diamonds, 200 simulants & 200 synthetics | Ø: 1 to 3.8 mm • Speed rate measured > 6’500 stones/h • all results available on: https://diamondproducers.com/assure/
| PAGE 4
| CONTEXT & CHALLENGES
SSEF continues to challenge the ASDI Two goals: 1. Make ourselves small synthetic diamonds (RB, Ø: 1.5 - 2.0 mm)
with a low [N] would possibly enter inside the D-J colour range will measure their SWUV transparency
2. Predict the relation between colour grade and SWUV transparency
for natural and synthetic diamonds
D-J colour range???
T (%) = 100(I/I0) Abs = -log10(T/100)=log10(I0/I)
| PAGE 5
| RECUT OF A HPHT SYNTHETIC DIAMOND
97768 | FTIR spectrum
97768 | Nitrogen concentration
Selection of a HPHT synthetic diamond: Round brilliant cut Ø = 5.2 mm Specifically low [NC]: 1.9 ppm (C centres)
| PAGE 6
| RECUT OF A HPHT SYNTHETIC DIAMOND
97768 | Recut sketch
A new challenge: Recut the selected synthetic into 3 stones of different diameters A recut project
Ultra-Precise Laser Machining Center 5-axis Laser system for 3-D applications
A very precise and extremely thin (25 µm) sawing process
| PAGE 7
| RECUT OF A HPHT SYNTHETIC DIAMOND
The 5.2 mm stone sawn at half height of pavillion
SYNOVA | Water Jet Guided Laser Technology Sawing optical positionning & results
Julien Le Clec’ch, process engineer, SYNOVA
97768 A | 97768 B | 97768 C
A 3.0 mm
B 2.0 mm
C 1.5 mm
97768 | Cut-off pieces
| PAGE 8
| RECUT OF A HPHT SYNTHETIC DIAMOND
Mr. Bischoff, Geneva Polishing was finalized on a traditional scaife
C: boiled in acid, unpolished (no crown, need to be recut)
A & B: after facetting & polishing
A B
C
C
| PAGE 9
| COLOUR vs SIZE Colour measurement on SSEF “ASDI - CGM” Colorimeter daily used at SSEF for three years now
SSEF Gem Color Analyzer For RB, Ø: 1.0 mm to 6.6 mm
| PAGE 10
| COLOUR vs SIZE Colour measurement on SSEF “ASDI - CGM” Colorimeter daily used at SSEF for three years now
SSEF Gem Color Analyzer For RB, Ø: 1.0 mm to 6.6 mm
| PAGE 11
| COLOUR vs SIZE Colour measurement on SSEF “ASDI - CGM” Colorimeter daily used at SSEF for three years now
SSEF Gem Color Analyzer For RB, Ø: 1.0 mm to 6.6 mm
| PAGE 12
| COLOUR vs SIZE 97768 | Colour measurement on SSEF “ASDI - CGM”
Date, Time
Host Application
Number of Measurements
Sample Name
L* L* STD a* a* STD b* b* STD
103.4152 0.4780 -2.1697 0.2366 6.2871 0.5729
Transmission Measurement Mode: Automatic 360° Rotation
AVERAGED Color Measurement Data (CIE, D6500)
OK97768
Y-Scaling Factor 1.0000
22.11.2018 08:44:46
Revision 3.0.2 | March 2018
72
-8
-6
-4
-2
0
2
4
6
8
-5 -3 -1 1 3 5
BLU
E <-
-b
* --
> YE
LLO
W
GREEN <-- a* --> RED
GCA Transmission AVERAGED Color (a*, b*)
-8
-6
-4
-2
0
2
4
6
8
90.0 95.0 100.0 105.0 110.0
BLU
E <
--b
* --
> YE
LLO
W
DIM <-- L* --> LIGHT
GCA Transmission AVERAGED Color (L*, b*)
| PAGE 13
| COLOUR vs SIZE 97768, 97768 A & 97768 B | compared to SSEF master-stones
97768 C not plotted, Luminance out of range ( L*=76.0195)
F G
H
J
L
97768 (5 mm)
97768 A (3 mm)
97768 B (2 mm)
1.0
3.0
5.0
7.0
9.0
11.0
13.0
15.0
-6.0 -4.0 -2.0 0.0 2.0
BLU
E <
-- b
* -->
YE
LLO
W
GREEN <-- a* --> RED
R
Z
| PAGE 14
A B
C
| COLOUR vs SIZE An apparent contradiction: “The colour of the 3 mm recut stone is much lighter than that the 2 mm recut stone.”
Theoritically, the thinner the lighter.
So the 3 mm stone is lighter than 2 mm?
| PAGE 15
A B
C
| COLOUR vs SIZE An apparent contradiction: “The colour of the 3 mm recut stone is much lighter than that the 2 mm recut stone.”
Because the distribution of the yellow colour (C centres) inside the grown crystal is inhomogeneous.
Its core is colourless and its rim is yellow
Theoritically, the thinner the lighter.
So the 3 mm stone is lighter than 2 mm?
The larger stone (A) cut at the centre of the crystal, is colourless (G colour grade) The smaller stone (B) cut at one summet of the crystal, is yellow (S-Z)
| PAGE 16
97768 A (G colour) | SWUV transmission (ASDI) & Absorption coefficient
0
1
2
3
4
5
6
230 330 430 530 630 730
(270 nm; 2.5 cm-1, [N°S]=2.5 ppm, G colour)
| SWUV TRANSMISSION vs SIZE
97768 A (3.0 mm) REFERRED FOR ITS SWUV TRANSPARENCY (7.5 V)
7.5 V
Ab
sorp
tio
n c
oef
ficie
nt
(1/c
m)
| PAGE 17
97768 B (S-Z, out of ASDI spec) SWUV absorption coefficient
| SWUV TRANSMISSION vs SIZE
0
2
4
6
8
10
12
14
230 330 430 530 630 730
(270 nm; 14.3 cm-1, [N°S]=14.0 ppm, S-Z colour)
Ab
sorp
tio
n c
oef
ficie
nt
(1/c
m)
Reference Ø
(mm) CIE (L*a*b*)
Colour Grade
Transmission (1) @ 270 nm
Absorption coefficient @ 270 nm
97768 5.2 (103.4152, -2.1697, 6.2871) M-R NA 4.9 cm-1
97768 A 3.0 (101.4331, -0.1404, 1.5446) G 7.5 V 2.5 cm-1
97768 B 2.0 (98.6827, -3.0896, 7.8891) S-Z 0.2 V 14.3 cm-1
(1) Voltage measured by the ASDI device NA: Not Applicable due to the size out of specifications
| PAGE 18
| NORMAZILED SWUV TRANSMISSION vs YELLOW COLOUR 1. for SYNTHETICS (Ib) (needs more data)
| PAGE 19
| NORMAZILED SWUV TRANSMISSION vs YELLOW COLOUR 2. for NATURALS (Ia) & SYNTHETICS (Ib) (needs more data)
| PAGE 20
| NORMAZILED SWUV TRANSMISSION vs YELLOW COLOUR 3. for NATURALS (Ia) & SYNTHETICS (Ib) as tested by ASDI
| PAGE 21
| CONCLUSION
OPTICAL PROPERTIES Inhomogeneous distribution of colour in a HPHT synthetic diamond of low [N] Relationship between colour & SWUV transmission for synthetics and naturals
SWUV transmission remains an efficient method for fast screening of D-J melee diamonds
For more data, we will soon recut two additional HPHT synthetic diamonds with low [N]
| PAGE 22
| THANK YOU
CO_AUTHOURS Ly Phan1, Michael S. Krzemnicki1, Hao Wang1
Jörg Pausch2, Julien Le Clec’ch2
Michael Steinacher3 (1) Swiss Gemmological Institute SSEF, Basel, Switzerland (2) Synova SA, Duillier, Switzerland (3) Department of Physics, University of Basel, Basel, Switzerland
Michael Steinacher fine tuning the ASDI machine
SPECIAL THANKS TO Stephan Bischoff, STEN Sarl, Geneva Pierre Lefèvre, Luc Pan & Vito Lanzafame, SSEF
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