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An analysis of synthetic ruby overgrowth on corundum

June 2015

Authors:

Sudarat Saeseaw

Gemological Institute of America

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The report indicates the status of a research project that is still ongoing within GIA Laboratory Bangkok.

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Please contact: giabkklab@gia.edu stating the name of the project and name(s) of the author(s).

NEWS FROM RESEARCH

An analysis of synthetic ruby

overgrowth on corundum

Sudarat Saeseaw, Vincent Pardieu, Vararut Weeramonkhonlert,

Supharart Sangsawong and Jonathan Muyal

Wafers showing the synthetic ruby at the edge and natural seed at the center. Photo by J. Muyal © GIA.

Table of Contents

Table of Contents ................................................................................................................................................................ 2

Introduction .......................................................................................................................................................................... 3

Materials and Methods........................................................................................................................................................ 4

Examination Results ............................................................................................................................................................ 5

Microscopic examination ............................................................................................................................................... 5

Type I: Stones 385, 386 and 390 with no obvious interface between natural seed and the synthetic layer

........................................................................................................................................................................................ 5

Type II: Stones 387, 384, 392, 391, 389, 393, 388, with clear dusty interface between the natural and

synthetic layer .............................................................................................................................................................. 9

Chemistry .......................................................................................................................................................................... 9

Type I: the chemistry of sample 385 (Figure 7 and Table 2). .......................................................................... 10

Type II: sample 391 was selected in this study (Figure 8 and Table 3). ......................................................... 11

Duros and hydrothermal synthetic ruby samples ............................................................................................... 12

Infrared Spectroscopy ................................................................................................................................................... 13

Observations ........................................................................................................................................................................ 15

Biography ............................................................................................................................................................................. 15

©GIA http://www.giathai.net June 10th 2015

Introduction

Synthetic ruby is one of the most commonly synthesized gems with various methods being used since the

turn of the last century (Scarratt 1977, Bank and Schmetzer 1979, Schmetzer and Bank 1988, Peretti and

Smith 1993, Scarratt 1994, Muhlmeister, Fritsch et al. 1998, Shida. 2000). The synthetic overgrowth of ruby

on corundum seeds is one of the rarer versions of these processes, however, it is not particularly new and

indeed such materials were reported relatively recently by GIT (Promwongnan. 2015)

This additional report characterizes the material further and adds detailed chemical analyses to the data

already published.

In 2014 author VP acquired ten specimens in which it was stated that synthetic ruby have been overgrown

onto natural corundum, these were obtained via Laurent Massi who in turn had purchased them from Karim

Guercouche of Premacut Ltd, a Bangkok based supplier. It was indicated to VP that the stones in questions

were related to attempts during the early 1990’s to diffuse Cr into natural pink sapphires and thereby change

their color appearance to that of ruby. Indeed after disappointments in the Cr diffusion experiments (Smith

2002)some colorless sapphires of Sri Lankan origin were given to the Duros Company, famous for their

synthetic rubies (Hänni 1993, Koivula and Fritsch 1993, Hänni and Schmetzer 1994, Hänni, Schmetzer et

al. 1994, Hänni, Schmetzer et al. 1994), for further experiments and the specimens reported upon here are

reportedly (quality) rejects from these experiments with Douros.

©GIA http://www.giathai.net June 10th 2015

Materials and Methods

Table 1: The reference number and weight of the “synthetic overgrowth” ruby Samples used in this study (see also Figure 1 and Figure 2)

Reference #Type I Weight

(carats) Image

100310677385

1.406

100310677386

1.773

100310677390

1.765

Reference # Type II Weight

(carats) Image

100310677384

1.996

100310677387

1.421

100310677388

1.904

100310677389

2.091

100310677391

2.173

100310677392

2.073

100310677393

1.873

Ten faceted samples of synthetic overgrowth ruby were used for this report (Table 1) which were obtained

from Premacut Ltd., a Bangkok based gemstone supplier. The stones ranged in size from 1.40ct to 2.17ct

and were either near round or oval in shape. The color of the samples ranged from purplish red to red.

Standard gemological testing was carried out using the OPL hand held spectroscope to establish that the

material was indeed ruby.

Internal features were observed using a variety of Gemolite microscopes with magnifications ranging up to

70x, and a Nikon SMZ 1500 system with darkfield, brightfield, and diffused illuminations, together with a

fiber-optic light source when necessary with magnifications and photo imaging of up to 180x.

FTIR microscopy was performed using a Nicolet iN10 (Thermo Fisher Scientific) operating in a reflection

mode with a liquid nitrogen cooled MCT-A (mercury cadmium telluride) detector and a KBr beam-splitter.

The iN10 conditions used were at 4 cm-1 spectral resolution, 128 scans, and aperture size of 150 X 150 um.

Three samples (385, 386 and 391) were cut into wafers for inclusion and chemical analysis.

Chemistry was performed using Thermo Fisher Scientific iCAP Q Induced Coupled Plasma - Mass

Spectrometer (ICP-MS) coupled with a Q-switched Nd:YAG Laser Ablation (LA) device operating at a

wavelength of 213 nm. Laser conditions used 55 μm diameter laser spots, a fluency of around 10 J/cm2, and a

15 Hz repetition rate. For the ICP-MS operations, the forward power was set at ~1350 W and the typical

nebulizer gas flow was ~0.80 L/min. The carrier gas used in the laser ablation unit was He, set at ~0.50

L/min. The criteria for the alignment and tuning sequence were to maximize beryllium counts and keep the

ThO/Th ratio below 2%. A special set of synthetic corundum reference standards (Be, Mg, Ti, Cr, V, and

Ga-doped) and a natural sample for Fe were used for quantitative analysis. All elemental concentrations were

calculated by applying 27Al as an internal standard, with Al concentration calculated from the theoretical

value of corundum (52.92 wt%)

Examination Results

For convenience and based only upon microscopic observations the samples in this study (Table 1) were

separated into two ‘types’: Type I and Type II. The separation was simply related to whether or not the

interface between the synthetic overgrowth and the ‘natural sapphire seed” was easily visible using a standard

gemological (Gemolite) microscope. Type I consisted of three samples where there was no obvious interface

visible while type II consisted of seven samples where there was a clear ‘dusty’ interface

Observed with the unaided eye, the color of all samples appeared the purplish red to red that is expected for

natural rubies. However, the type II samples (Figure 2 bottom) appeared more homogenous in color than

type I (Figure 2 top) samples. The type I samples had a very thin layer of synthetic ruby overgrowth forming

the table with most of the other areas of the samples having no overgrowth on the seed material. In contrast,

a thicker layer of synthetic overgrowth was observed in type II samples.

Standard gemological properties of these stones were normal for corundum. Under long-wave ultraviolet the

samples appeared to fluoresce from a strong red to being inert and were inert to chalky in some areas under

short-wave.

Microscopic examination

Type I: Stones 385, 386 and 390 with no obvious interface between natural seed and the

synthetic layer

Three stones (#385, 386 and 390) were examined using a Gemolite microscope. The features noted at the

interface between the natural seed and the synthetic outer layers were triangular growth marks (Figure 2a),

sub-parallel striations (Figure 2b) and ‘mountain peak’ or ‘heat wave-like’ formations (Figure 2c). In the

©GIA http://www.giathai.net June 10th 2015

{Face up

{Face Down

Type II

outer layer of synthetic overgrowth flux healed fissures (fingerprints) (Figure 2d) and a frosted crystal-like

inclusion (Figure 2e) were observed.

{Face up

{Face Down

Type I

Figure 1: GIA reference sample: Type I (385, 390, 386 from left to right) and type II (387, 384, 392, 391 (top) and 389, 393, 388 (bottom)).

Photo by N. Kitdee © GIA.

©GIA http://www.giathai.net June 10th 2015

Figure 2: a) Triangular growth marks on the surface in sample 385, magnified 40x; b) subparallel striations, magnified 64x; c) triangular or wavy like

striations, magnified 50x – see also the surface of the hydrothermal crystal in Figure 13; d) flux fingerprint, magnified 60; and e) frosted crystal, magnified

70 in sample 386, can be seen in the synthetic ruby overgrowth of type I samples. Photo by J. Muyal © G IA.

Within the natural seeds in samples #385, 386 and 390 the features noted were naturally healed fractures

(Figure 3, a & b), heat altered crystals (Figure 3c), intersecting needles (rutile) (Figure 3d), and ‘particle

stringers’ (Figure 3e).

As there seemed to be no obvious interfaces between the natural seed and the synthetic overgrowth with

these three samples, samples 385 and 386 were immersed in methylene iodide and their growth structures

examined using a horizontally oriented immersion microscope. Both samples were oval in oval shape (Figure

4a & c), however, in immersion the natural seed in sample 385 was found to be heart shape (Figure 4a) and

no obvious natural seed was seen in sample 386 (Figure 4c). When the samples were cut across the width into

wafers, a thin layer of synthetic ruby overgrowth was clearly seen in sample 385 (Figure 4b); whereas a much

thicker layer was seen in sample 386 (Figure 4d), particularly at the culet.

©GIA http://www.giathai.net June 10th 2015

Figure 3: a), b) naturally healed fractures in sample 385, magnified 50x and in sample 390, magnified 30, respectively; c) altered crystal with healed

fracture in sample 389, magnified 70x; d) needles in sample 385, magnified 50x; and e) stringers in sample 386, magnified 40x can see in natural seed of

type I samples. Photo by J. Muyal © GIA

Samples 385 & 386 below photographed immersed

in methelyne iodide as faceted stones

Samples 385 & 386 below photographed in color

corrected conditions after being cut into wafers

Sample 385

Sample 386

Figure 4: Sample 385 (top) and sample 386 (bottom). Photo by S. Saeseaw and S. Engniwat © GIA.

Table

Culet

©GIA http://www.giathai.net June 10th 2015

Type II: Stones 387, 384, 392, 391, 389, 393, 388, with clear dusty interface between the

natural and synthetic layer

Seven stones, # 387, 384, 392, 391, 389, 393 and 388 showed very clear demarcation between the natural

seed and the synthetic overgrowth, the interface appearing what might best be described as “dusty”. The

synthetic layer had the appearance of being ‘cracked’ and contained many coarse flux inclusions (Figure 5).

This type of sample while appearing homogenous to the unaided eye, appeared very ‘cracked’ under

magnification and in dark field illumination (Figure 5a, b and c). The inclusions observed in the natural

seeds included blue color zoning (Figure 5b), altered crystals (Figure 6a) and altered fingerprints (Figure 6b).

Sample 389 was cut through and showed many particles in the form of ‘stringers’ (Figure 6c). In general the

synthetic overgrowth in the type II samples was relatively thick, making the samples appear more

homogeneous in color and giving them a more natural appearance.

Figure 5: Sample 389 taken under a) dark filed illumination and b) diffuse light illumination, magnified 7.5x; c) flux inclusions reaching to the surface,

magnified 35x can be seen in all seven samples on the synthetic ruby overgrowth of type II samples. Photo by J. Muyal © GIA

Figure 6 a) altered crystals with healed fractures in sample 391; b) altered fingerprints in sample 388; and c) wafer sample 389 showed particles and

stringers, magnified 15x can see in natural seed of type II samples. Photo by J. Muyal © GIA

Chemistry

Samples 385, 386 and 389 were fabricated into wafers in order to facilitate the determination of the

chemistry for both the seed material and the synthetic overgrowth, the analysis being carried out by LA-

ICPMS. It is interesting that the two types showed different chemistry as described below.

©GIA http://www.giathai.net June 10th 2015

Type I: the chemistry of sample 385 (Figure 7 and Table 2).

In sample 385 the synthetic ruby overgrowth revealed up to 6784 ppma of chromium (Cr) and no vanadium

(V), iron (Fe), nickel (Ni), zinc (Zn), gallium (Ga), or lead (Pb) were detected. However, the heavy elements

such as molybdenum (Mo), rhodium (Rh), platinum (Pt) were clearly evident in the analysis. A small

amount of iron (Fe) was detected in the analysis of spots 5 and 6 but this was due to the laser spots

encompassing both the synthetic overgrowth and the natural seed areas.

At the center the natural seed of sample 385 magnesium (Mg), titanium (Ti), vanadium (V), chromium

(Cr), iron (Fe) and gallium (Ga)

which are typically present in natural

corundum, were clearly recorded

with the averages of Mg, Ti, and Fe

being 54, 82, and 72 ppma. The

average concentration of Ti-Mg was

approximately 28 ppma which in

theory should produce a blue color

when paired with Fe or Fe2+-Ti4+.

However, no blue color was observed.

Table 2: LA-ICP-MS results in parts per million atomic (ppma) units for GIA Type I reference sample 385. BDL” stands for “Below Detection Limit”

(analyzed in inclusions free area).

in ppma 9Be 24Mg 47Ti 51V 52Cr 55Mn 56Fe 60Ni 66Zn 69Ga 98Mo 103Rh 195Pt 208Pb

Synthetic ruby sp1

BDL

6784

BDL

4.57

0.58

3.08

BDL

Synthetic ruby sp2

BDL

6392

BDL

0.57

0.58

4.25

BDL

Synthetic ruby sp3

BDL

5529

BDL

2.95

0.38

1.09

BDL

Synthetic ruby sp4

BDL

4549

BDL

0.12

0.39

0.81

BDL

Synthetic ruby sp5 (boundary)

BDL

4863

BDL

0.42

0.31

0.71

BDL

Synthetic ruby sp6(boundary)

BDL

5725

BDL

1.08

0.40

0.84

BDL

Natural seed sp1

BDL

Natural seed sp2

BDL

Natural seed sp3

BDL

Natural seed sp4

BDL

Natural seed sp5

BDL

Natural seed sp6

BQL

BDL

Figure 7: Wafer of GIA reference sample 385 showing the location of the laser spots in

synthetic ruby at the edge and natural seed at the center. The photo was color calibrated

and captured using transmitted light. Photo: S. Engniwat © GIA

©GIA http://www.giathai.net June 10th 2015

Type II:

sample 391 was selected in this study (Figure 8 and Table 3).

In sample 391 the synthetic ruby overgrowth (red rim) recorded 10353 ppma of chromium (Cr) which may

be considered to be high. In common with natural corundum other elements such as magnesium (Mg),

titanium (Ti), vanadium (V), iron (Fe), and gallium (Ga) were also recorded. However, manganese (Mn),

nickel (Ni), zinc (Zn), and the heavy metal platinum (Pt) also had a significant presence in the chemistry of

the synthetic ruby overgrowth.

The trace element chemistry of the natural

corundum seed used in sample 391

included magnesium (Mg), titanium (Ti),

vanadium (V), chromium (Cr), iron (Fe)

and gallium (Ga). The average

concentration of Ti-Mg was about 18

ppma, however in common with type I

sample no blue color observed,. There were

no heavy elements detected in this area.

Figure 8

Wafer of GIA reference sample 391 showing the location of the laser spots in synthetic ruby at the edge and natural seed at the center. The photo

was color calibrated and captured using transmitted light. Photo: S. Engniwat © GIA.

Table 3: LA-ICP-MS results in parts per million atomic (ppma) units for GIA Type II reference sample 391. BDL” stands for “Below Detection Limit”

(analyzed in inclusions free area).

in ppma

9Be

24Mg

47Ti

51V

52Cr

55Mn

56Fe

60Ni

66Zn

69Ga

98Mo

103Rh

195Pt

208Pb

Synthetic ruby sp1

BDL

8863

1.4

313

1.1

1.0

BDL

0.08

BDL

Synthetic ruby sp2

BDL

8706

1.8

333

1.0

1.7

BDL

0.10

BDL

Synthetic ruby sp3

BDL

10353

1.5

335

1.3

2.2

BDL

0.11

BDL

Natural seed sp1

BDL

127

BDL

Natural seed sp2

BDL

129

BDL

Natural seed sp3

BDL

128

BDL

Natural seed sp4

BDL

127

BDL

Natural seed sp5

BDL

136

BDL

Natural seed sp6

BDL

127

BDL

Duros and hydrothermal synthetic ruby samples

Given the indications (statements made at the time of acquisition, see introduction) that the company that

produced the Douros synthetic ruby were involved in the production of these synthetic overgrowth rubies

and that the infrared spectra recorded at the interface of the overgrowth and the natural seed of a Type I

specimen revealed features close to those seen in hydrothermal synthetic rubies (Figure 10), for comparative

purposes the authors also collected chemistry from one known Douros (Figure 12) and one known

hydrothermally grown (Figure 13) synthetic ruby crystal.

For the hydrothermal synthetic (Table 4) the material appeared to be relatively free of ‘unusual’ trace

elements the exception being Ni with a presence of between 4 and 23 ppma. Mo, Rh, Pt and Pb were all

below the detection limits. Cr was present at the expected high levels but Fe was below detection limits as

were Ga and V. These data do not correlate well with either the Type I or the Type II synthetic ruby

overgrowth samples examined here.

For the Douros synthetic ruby crystal (Table 5) Ga was determined to be present at relatively high levels

(196-202ppma) but this is to be expected for this particular synthetic material (Hänni, Schmetzer et al.

1994). As expected Rh and Pb and in particular Pt were present in detectable amounts. Cr was detected and

relatively low levels in comparison to Fe. As with the hydrothermal synthetic the chemistry data of the

Douros synthetic ruby crystal do not correlate well with either the Type I or the Type II synthetic ruby

overgrowth samples examined here.

Table 4: LA-ICP-MS results in parts per million atomic (ppma) units for the Russian hydrothermally grown synthetic ruby depicted in Figure 13. BDL”

stands for “Below Detection Limit”.

Hydrothermal synthetic ruby

Spot #

9Be

24Mg

47Ti

51V

52Cr

55Mn

56Fe

60Ni

66Zn

69Ga

98Mo

103Rh

195Pt

208Pb

sp1

BDL

5.7

BDL

6157

BDL

sp2

BDL

0.9

BDL

4980

BDL

sp3

BDL

0.9

BDL

4902

BDL

sp4

BDL

0.6

BDL

5333

BDL

Table 5: LA-ICP-MS results in parts per million atomic (ppma) units for the Douros synthetic ruby depicted in Figure 12. BDL” stands for “Below

Detection Limit”.

Douros synthetic ruby

Spot #

9Be

24Mg

47Ti

51V

52Cr

55Mn

56Fe

60Ni

66Zn

69Ga

98Mo

103Rh

195Pt

208Pb

sp1

BDL

1.1

BDL

2.1

1194

BDL

196

BDL

0.03

sp2

BDL

1.3

BDL

2.0

1172

BDL

197

BDL

0.03

0.04

sp3

BDL

1.1

BDL

1.8

1209

BDL

202

BDL

0.02

0.03

sp4

BDL

0.8

BDL

1.6

1117

BDL

192

BDL

0.03

0.04

Infrared Spectroscopy

Type I samples presented interested FTIR spectra at the interface between natural seed and synthetic ruby

overgrowth with peaks at 3475 and 3355 cm-1 (Figure 10) neither of which were recorded in the bodies of

the natural seed or the synthetic overgrowth, indeed these other areas examined produced featureless IR

spectra. These features produced at the

interface were similar to but not the same as

those reported for some hydrothermally

grown synthetic rubies (Figure 11). At

present these features noted at the interface

are not understood and further work is

necessary before an attribution made.

Figure 10: The infrared spectra recorded for the natural seed (green) the synthetic ruby overgrowth (red) and at the interface between the seed and the

overgrowth (black) using a FTIR microscope (iN10).

3475 3355

0.1

0.2

0.3

0.4

0.5

0.6

300031003200330034003500360037003800

Absorbance

Wavenumber, cm-1

natural seed

interface

synthetic ruby

Figure 9: The areas from which infrared spectra were recorded (circled) and detailed

sample 386, from a Type I sample of synthetic overgrowth ruby. Photo:

Khowpong

Figure 13: A crystal of Russian grown hydrothermal synthetic ruby

and a wafer

from the same crystal

the IR spectrum of which can be

een in Figure 11. Photo by L. Nillapat (top) and

S. Engniwat

(bottom) © GIA

Figure 11: The IR spectra of a Douros synthetis ruby (Figure 12) and a wafer of Russian grown hyrothermally synthetic ruby (Figure 13) using a Nicolet

6700 FTIR spectrometer.

3561 3483 3304

4.5

5.5

0.5

1.5

2.5

300031003200330034003500360037003800

Absorption coefficient, cm

-1 (for Doros)

Wavenumber, cm-1

Doros

hydrothermal

Figure 12: A crystal of the Douros synthetic ruby the IR spectrum of

which can be seen in

Absorption coefficient, cm-1 (for hydrothermal)

Observations

The natural inclusions depicted as being present in the natural ‘seeds’ of this synthetic ruby overgrowth

material in Figure 3 might possibly mislead an observer into assuming that they were examining a natural

ruby, however, a careful examination should in all cases reveal the synthetic ruby overgrowth. The presence

of these natural inclusions though also give some insight into the growth conditions used in so much as the

temperatures used could not have exceed 1200°C. The inclusions recorded in the synthetic overgrowth ruby

were typical of what might be expected within a flux growth synthetic ruby -‘flux healed’ fissures and other

flux related inclusions, however, the triangular or wavy (heat-wave) like striations (Figure 2c) had a similar

appearance to the surface of the hydrothermal crystal depicted in Figure 13.

The infrared spectra proved to be interesting but only in terms of the spectra obtained at the interface

between the natural seed and the synthetic overgrowth. The synthetic overgrowth and the natural seed

themselves producing no discernible features whereas a series peaking at 3475 and 3355 were recorded from

the material at the interface that were reminiscent of (but not identical to) the series observed in

hydrothermally grown synthetic ruby.

The chemistry recorded for the samples indicated that differing growth conditions may have been applied for

the two types (Type I and Type II). Mo (often recorded in flux grown synthetic rubies) was clearly present in

the synthetic overgrowth of type I but not in Type II samples whereas Ni was recorded in Type II specimens

but not in Type I. Ga and V were not evident in the synthetic overgrowth ruby in Type I but clearly present

in the overgrowth of Type II specimens – previous reports on Douros synthetics have reported the clear

presence of Ga.

Both types contained a significant Pt content, but Rh was detected in type I samples only.

In the cases where inclusions or other growth indicators are not evident the detection of the elements Pt, Rh,

Ni, or Mo would prove useful in identifying specimens as being of synthetic origin. However, analyses using

LA-ICP-MS would be necessary.

Bibliography

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synthetischem korund." Zeitschrift der Deutschen Gemmologischen Gesellschaft 28(3): 148-149.

Hänni, H. A. (1993). "A new synthetic ruby from Greece poses challenges for gemologists." Rapaport

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Hänni, H. A. and K. Schmetzer (1994). "How to identify Douros synthetic rubies." Jewellery News Asia:

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Hänni, H. A., et al. (1994). "Synthetic rubies by Douros: A new challenge for gemologists." Gems and

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Hänni, H. A., et al. (1994). "Synthetische rubine von Douros." Goldschmiede Zeitung(11): 101-108.

Koivula, J. I. and E. Fritsch (1993). "Douros flux-grown synthetic ruby." Gems and Gemology 29(4): 295.

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chemistry." Gems and Gemology 34(2): 80-101.

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rubies from Novosibirsk." Australian Gemmologist 18(5): 149-156.

Promwongnan., S., Saengbuangamlam., S, Leelawatanasuk (2015) Lab Update - Synthetic Ruby Overgrowth

on Natural Corundum. GIT

Scarratt, K. (1977). "A study of recent Chatham synthetic ruby and synthetic blue sapphire crystals with a

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Scarratt, K. (1994). "Lab Report: Kashan synthetic rubies; synthetic ruby from Russia; hydrothermal

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Schmetzer, K. and H. Bank (1988). "Lechleitner synthetic rubies with natural seed and synthetic

overgrowth." Journal of Gemmology 21(2): 95–101.

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ResearchGate has not been able to resolve any citations for this publication.

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