A New Technique for the Analysis ofCorundum Using Laser Ablation ICP-MS
Application

Gemology

Author
Ahmadjan Abduriyim, Hiroshi Kitawaki, Junko Shida, FGA, CGJ
Gemological Association of All JapanTokyo, JapanAbstract
A large percentage of rubies and sapphires undergo somedegree of heat treatment to enhance their color and, as aresult, to increase their value. As the majority of “processors” certify their gems as “heat treated”, this practice is
accepted by the trade. Established treatment methods
involve super-heating the gems to near melting point,around 2000 °C, and diffusing them with hydrogen. Dealers have established analytical methods to differentiatethese stones from untreated natural or synthetic ones.
With the market value of natural sapphires far outweighing that of both synthetic stones and natural gems thathave undergone color-enhancing processing, it is important to be able to make this distinction. However, a newprocessing technique was developed that involves theaddition of beryllium (Be) during the heat treatment
stage, making the treated stones very difficult to identify.
This technique has been applied to modify some corundum to resemble one of the most valuable colored stones:
vivid orange-yellow gems known as padparadscha.
Because some processors refuse to disclose the gems as“beryllium-diffused”, referring to them only as "heattreated", and because beryllium is difficult to detect by
conventional gemological instrumentation, the price anddemand for colored stones has weakened [1].

Researchers at the Gemological Association of All Japan
found that laser ablation inductively coupled plasma
mass spectrometry (LA-ICP-MS) is an extremely effective means of investigating the distribution of Be, andother impurity elements, across the surface of a finishedgem. This information allows gemologists to identify thedifferent types of processing that has been applied toindividual sapphires. However, more research is required
to understand the physical mechanisms that give rise to
the color enhancements.

Introduction
Rubies and sapphires belong to the group of gemstones known as “Corundum”, which is the gemological name for aluminum oxide (Al2O3). Red (andmost pink) corundum is known as ruby. Many different colors of corundum occur, the color being
derived from the trace metal content (for example,
it is the presence of chromium that gives rubies
their bright red color). While many people associate sapphires with the color blue, highly saturated
orange, pink and yellow gems are widely available
on the market and these are named according totheir color, for example, yellow sapphire. Amongthese colored sapphires is one of the most valuable
colored stones, a rare orange-pink gem known as“padparadscha”, whose color appears even andvivid. Because of the high market value of natural
padparadscha, there is concern about a newprocess which, when applied to certain lower
value natural sapphires, could produce stones thatare extremely difficult to distinguish from natural
padparadschas. The new treatment involves heating stones with beryllium (Be) powder which,when diffused into the corundum, enhances thecolor of yellow stones. Laboratory studies ofenhanced stones have shown the orange-yellow
layer forms only on the outer rim of the stonealong the faceted surface, while the center isalmost pink. Similarly, violet, green, or blue sapphires are available in which a yellow or orange
layer forms on the outer rim along the faceted surface. Because of this unusual color distribution, it
was suspected that these modified stones had
undergone a type of “ diffusion” treatment. Initialstudies revealed that the heat process used(referred to as a “new heat process”) causes Be to
diffuse into the corundum.
Several different explanations have been proposedto account for the coloring mechanism, but one difficulty has been the detection of Be by conventional gemological instruments. In this study,
LA-ICP-MS was used to analyze impurity elements,
including Be, present in unheated, heat-treated,and synthetic corundum samples.

Samples and Methodology
To evaluate the new Be-diffused heat process, “finished” stones were analyzed, using LA-ICP-MS,
both before and after treatment by the “new heatprocess”. Samples included:• Colorless verneuil-processed synthetic sapphire(traditional flame-fusion process)• Pieces of flux-grown synthetic pink sapphire

The samples were treated using the Be-diffusedheat method by processors in Bangkok and Chanthaburi in Thailand. The stones were put into acrucible together with chrysoberyl (Be aluminumoxide) and heated at over 1800 °C in an oxidizing
atmosphere for 22 and 10 hours, respectively.
To assess the accuracy of the LA-ICP-MS results, arepeat analysis was done on each sample using
secondary ion mass spectrometry (SIMS).
LA-ICP-MS
LA-ICP-MS is widely used to determine elements
directly in solid samples with minimal sample
preparation. It is a highly sensitive multi-element
technique with a wide analytical dynamic range
from ppt to ppm-level in the solid. For this study, aMerchantek UP-213 (New Wave Research. Inc,USA) LA system was coupled to an Agilent 7500a
ICP-MS. A schematic of the laser ablation system isshown in Figure 1. The sample surface is irradiated with deep-UV (213 nm) output from afrequency-quintupled Nd:YAG (neodymium doped
yttrium aluminum garnet crystal) laser. The laser
light couples to the surface of the sample, causing
very rapid heating which, in turn, causes thematrix to be volatilized or ablated. This ablatedmaterial is then carried to the ICP-MS in an argon
carrier gas stream for analysis. Calibration is typically against a well-characterized synthetic solidmaterial, such as NIST 612 Trace Elements inGlass.

• Natural sapphires of each color

CCD Camera

Motorized zoomMonitor
FilterNd: YAG Laser

Beam expander

Energy probe
Light source

Objective lensSolenoidvalve
To ICPAr inTranslation stage
Purge

Polarized lightsource

Figure 1.
2

Schematic of Nd: YAG laser ablation system (5th harmonic - 213 nm) for ICP-MS.

Results and Discussion
LA-ICP-MS measurements of Be in unheated andtraditionally heat-treated corundum of each color(40 pieces in total) are shown in column 2 ofTable 1. Beryllium was present below the background level of the instrument in all of thesesamples.
Table 1.

LA-ICP-MS Analysis of Be in Sapphires of Each Color
Unheated or“traditional” heatprocessed, Be, ppm

Number ofsamples“New” Be-diffusedprocess, Be, ppm

Number ofsamples

Yellow<0.035

4

1.79-8.09

8Padparadscha<0.002

2

1.54-4.36

10

Orange<0.0484

1.95-4.14

7

Pink<0.0334

1.92-3.27

4

Purple<0.0082

2.63-7.79

10

Blue

<0.0125

1.43-14.9

20

Color change<0.0162

1.71-2.56

2Colorless<0.003

5

0.57-1.394Ruby<0.01520.43-15.7

4

Colorless<0.029 (Unheated)

100.32-5.03

8Pink––

0.27-1.73

2

Natural Stones

Synthetic Stones

Total number of samples

4079However, Be (in the order of several ppm) wasdetected in all corundum, natural and synthetic,that were heated in the new process (79 pieces), as
shown in column 3 of Table 1. Trace elements thatare commonly seen in corundum, such as Ti, V, Cr,Mn, Fe, Ga, and Al, the main constituent element,
were also detected by LA-ICP-MS (results notshown).

3Further investigation suggested that the concentration of Be was higher in stones heated for alonger period (the “Bangkok” treatment, over22 hours) than those heated for a shorter period(the Chanthaburi process, 10 hours). Figure 2 summarizes Be data obtained from LA-ICP-MS analysis
of colorless synthetic and colorless natural sapphires treated over 10 hours and 22 hours, respectively. The graphs illustrate the change in Be
concentration across cut surfaces of the samples
and indicate significant differences in thedistribution of the element.
There was no color alteration in either the naturalor synthetic samples that were treated for
10 hours; however, with the 22-hour heat process,while there was no color change for the colorless
synthetic sapphires, the colorless naturalsapphires became yellow.

Edge

Edge
Concentration of Be (ppm)

5Be

422 h heated
12 h heated

32
10
12

3

5

4

687

Point
Edge

Edge
Concentration of Be (ppm)

5Be

4

22 h heated
12 h heated

32
1012

3

54

678

Point

Figure 2.

4Distribution of Be across the cut surface of synthetic (top) andnatural (bottom) sapphires with different heating periods. The
length of the cut face analyzed was 500 µm for the synthetic and300 µm for the natural stone.

SIMS
SIMS is a sensitive elemental surface analysis technique suitable for local analysis. It is used to analyze light elements with sensitivity similar toLA-ICP-MS, but its operation is more complicatedand it requires a highly skilled operator. The SIMS
analysis was performed by the Foundation of Promotion for Material Science and Technology ofJapan using a Cameca IMS-6f magnetic sector
instrument (Paris, France).
Figure 3 shows the distribution profile of Be acrossthe cut surface of a padparadscha-colored sample(average 400 microns) that had undergone
Be-diffused processing. Both the LA-ICP-MS andSIMS results show a similar trend: a low concentration of Be in the center of the cut stone and ahigher concentration towards the outer rim. Different standard samples were used to calibrate thetwo analysis methods which account for the differences in the concentration values obtained; NIST
612 Trace Elements in Glass was used to calibrate
LA-ICP-MS and a “synthetic sapphire with addedberyllium” standard was used to calibrate theSIMS.

Concentration of Be (ppm)

108SIMSLA-ICP-MS

642012346578910PointFigure 3.

Be-distribution (400 microns) across a Be-diffused processedpadparadscha sapphire, measured using both SIMS andLA-ICP-MS. Note the SIMS result for points 5 and 7 is:0.0086 ppm.

5

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Conclusions

References

Beryllium was not detected in either unheated or
traditionally heat-treated crystals, but it was present in all sapphires of each color that were heatedin the new process. The results of the study suggest that some samples underwent a color change
as a result of the new heat-treatment processing
while some did not. Although Be itself does notdirectly cause the color change, it is thought thatthe interaction between the Be metal and othertrace transition elements (such as Fe), or between
the Be and defects (holes) in the crystal may produce the color change [2, 3]. As the color of somecrystals does not change, even when Be is dispersed during the new heat process, more clarification is needed to better understand themechanism at work.

1. Giving Orange a Bad Name, (2003) Colored
Stone 16, 2, p. 20 www.colored-stone.com
2. Mohapatra S.K.and Kröger F.A, Defect structureof a-Al2O3 doped with magnesium. (1977) Journal of the American Ceramic Society, 60,3–4, pp.141–148.
3. Emmett J.L.and Douthit T.R., Heat treating thesapphires of Rock Creek, Montana (1993) Gems& Gemology, 29, 4, pp.250–272.

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Investigation of the distribution of Be by LA-ICPMS is an extremely effective means to determine
whether a stone has undergone the new heatprocess or not. This is important to gemologists
who have no alternative method to determine
whether a batch of stones is natural or has beentreated using the new Be-diffusion method - vital
information to restore confidence in the market.
Furthermore, the LA-ICP-MS results were in good
agreement with the SIMS results.
This new method of heat treatment is expected todiversify in the future as other light element oxides
are used. In this case, LA-ICP-MS would be ideallysuited to detect Be and other light elements attrace levels in solid gemstones.

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© Agilent Technologies, Inc. 2004
Printed in the USA
June 28, 2004
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