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

Transcript of 36th International Gemmological Conference | August 2019 … · An apparent contradiction: “The...

Page 1: 36th International Gemmological Conference | August 2019 … · An apparent contradiction: “The colour of the 3 mm recut stone is much lighter than that the 2 mm recut stone.”

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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: 36th International Gemmological Conference | August 2019 … · An apparent contradiction: “The colour of the 3 mm recut stone is much lighter than that the 2 mm recut stone.”

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| 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: 36th International Gemmological Conference | August 2019 … · An apparent contradiction: “The colour of the 3 mm recut stone is much lighter than that the 2 mm recut stone.”

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| 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: 36th International Gemmological Conference | August 2019 … · An apparent contradiction: “The colour of the 3 mm recut stone is much lighter than that the 2 mm recut stone.”

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| 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: 36th International Gemmological Conference | August 2019 … · An apparent contradiction: “The colour of the 3 mm recut stone is much lighter than that the 2 mm recut stone.”

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| 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: 36th International Gemmological Conference | August 2019 … · An apparent contradiction: “The colour of the 3 mm recut stone is much lighter than that the 2 mm recut stone.”

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| 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: 36th International Gemmological Conference | August 2019 … · An apparent contradiction: “The colour of the 3 mm recut stone is much lighter than that the 2 mm recut stone.”

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| 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: 36th International Gemmological Conference | August 2019 … · An apparent contradiction: “The colour of the 3 mm recut stone is much lighter than that the 2 mm recut stone.”

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| 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: 36th International Gemmological Conference | August 2019 … · An apparent contradiction: “The colour of the 3 mm recut stone is much lighter than that the 2 mm recut stone.”

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| 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: 36th International Gemmological Conference | August 2019 … · An apparent contradiction: “The colour of the 3 mm recut stone is much lighter than that the 2 mm recut stone.”

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| 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: 36th International Gemmological Conference | August 2019 … · An apparent contradiction: “The colour of the 3 mm recut stone is much lighter than that the 2 mm recut stone.”

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| 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: 36th International Gemmological Conference | August 2019 … · An apparent contradiction: “The colour of the 3 mm recut stone is much lighter than that the 2 mm recut stone.”

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| 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*)

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| 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: 36th International Gemmological Conference | August 2019 … · An apparent contradiction: “The colour of the 3 mm recut stone is much lighter than that the 2 mm recut stone.”

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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?

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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)

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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: 36th International Gemmological Conference | August 2019 … · An apparent contradiction: “The colour of the 3 mm recut stone is much lighter than that the 2 mm recut stone.”

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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

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| NORMAZILED SWUV TRANSMISSION vs YELLOW COLOUR 1. for SYNTHETICS (Ib) (needs more data)

Page 19: 36th International Gemmological Conference | August 2019 … · An apparent contradiction: “The colour of the 3 mm recut stone is much lighter than that the 2 mm recut stone.”

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| NORMAZILED SWUV TRANSMISSION vs YELLOW COLOUR 2. for NATURALS (Ia) & SYNTHETICS (Ib) (needs more data)

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| NORMAZILED SWUV TRANSMISSION vs YELLOW COLOUR 3. for NATURALS (Ia) & SYNTHETICS (Ib) as tested by ASDI

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| 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: 36th International Gemmological Conference | August 2019 … · An apparent contradiction: “The colour of the 3 mm recut stone is much lighter than that the 2 mm recut stone.”

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| 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