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Conference Paper

Conference Paper

Experimental Study on Heat Treatment of Semitranslucent-opaque Sapphire from Chanthaburi, Thailand

Research Article

Conference Paper

The 7th International Gem and Jewelry Conference (GIT2021), Chanthaburi, Thailand

Experimental Study on Heat Treatment of Semitranslucent-opaque Sapphire from Chanthaburi, Thailand

By Tasnara SripoonjanBhuwadol Wanthanachaisaeng, Papawarin Ounorn, Nantharat Bunnag, Puksinee Kheawthuen and Chakkaphan Sutthira

2022, February 28

Figure1. The representative sample is split into three sections for heating experiments

Abstract
Chanthaburi, eastern Thailand, is one of the world-renowned gemstones producers. It is designated as a “City of Gems” as most of the world’s gemstones pass through the city. Chanthaburi has long been known for high-quality gemstones derived from basalt-related deposits (e.g., Bang Ka Cha, Khao Wua, Khao Ploi Waen), especially natural yellow sapphire–Mekong Whisky color–which is unparallelly unique. The important studies (e.g., Hughes, 2002; Emmett et al., 2003) previously found that an application of lattice-diffusion heat treatment with beryllium could predominantly produce attractive colors, such as yellow, yellowish orange, in many types of sapphire. This made unmarketable sapphires could be modified to a characteristic golden-yellow color and used in fine jewelry (Figure 1). However, the supply of those raw materials has been substantially reduced and is presently deficient. The semitranslucent-opaque sapphires (Figure 1) have been discovered to substitute the original unmarketable ones, otherwise, they were often cut as a cabochon to exhibit dark color with asterism, aka black star sapphires. The dark body color, as well as almost opaque transparency, is characterized by high Fe-rich content and densely exsolved silks of hematite and/or in part other Fe-Ti oxides (Saminpanya, 2001; Sripoonjan et al., 2013, 2014) resulting in poor diaphaneity of these sapphires. In recent years, the proliferation of new treatments provided great potential for improving gemstone quality, the less valuable sapphire can potentially turn into intense and stable yellow sapphire applying beryllium-assisting treatment (Be-heating). This study aims to carry on an experiment of lower quality semitranslucent-opaque sapphires treatment and to investigate the cause of changes in color and clarity.
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Affiliation:
1. G-ID Laboratories, Bangkok, 10120 Thailand
2. College of Creative Industry, Srinakarinwirot University, Bangkok, 10110 Thailand
3. The Gem and Jewelry Institute of Thailand (GIT), Bangkok, 10500 Thailand
4. Faculty of Gems, Burapha University, Chanthaburi, 22170 Thailand
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Conference Paper

The Study on CVD Synthetic Diamond from Various Producers

Research Article

Conference Paper

The 7th International Gem and Jewelry Conference (GIT2021), Chanthaburi, Thailand

The Study on CVD Synthetic Diamond from Various Producers

By Montira Seneewong-Na-Ayutthaya, Waratchanok Suwanmanee, Thanapong Lhuaamporn, Supparat Promwongnan, Nattapat Karava, Yadawadee Kowinthaweewat, Kannatee Fueangaksorn and Tasnara Sripoonjan

2022, Feb 28

Figure 1: The representative of CVD-grown diamond samples from India, China, and the United State for this study are shown here. They range from 0.3 to 0.1 ct. Photo by M. Seneewong-Na-Ayutthaya

Abstract
In the past decade, the diamond industry has been facing a new challenge as synthetic diamond (i.e., LGD orLaboratory-grown Diamond) become commercially available as gem grade and present a new natural diamond alternative besides diamond simulants that had already been available in the trade for several decades. While the emergence of the synthetic diamond market is not a concern itself, the mixing of synthetic diamonds and natural diamonds in the same batch can have a negative impact on the confidence of the entire supply chains in the jewelry industry.

Currently, there are two main crystal growth processes of the gem-quality synthetic diamond, namely the High Pressure and High Temperature or HPHT-grown and the Chemical Vapor Deposition or CVD-growth diamonds. In the last several years, the CVD synthetic diamonds have been gaining popularity in the market, especially in the melee-size diamond market and has often beenfound mixed with natural diamond parcels sold in the market. In 2021, the CVD production rose to 8 million carats of gem-quality material and there are expectations that the trend would move upwards continuously. China, India, and the United States are currently the world’s largest producers of CVD-grown diamonds. The most common CVD method used is Microwave Plasma Chemical Vapor Deposition (MPCVD) for growing single-crystal synthetic diamonds. Therefore, the current situation regarding CVD-grown diamonds raises concern over their identifiability, especially with those of the melee size.

In this research, the gemological and spectroscopic properties of CVD synthetic diamond samples produced from China, India, and the United States were examined to search for a suitable detection technique. The basic gemological analysis such as internal features analysis by gem-microscope, UV-fluorescence tester, and cross polar filter (CPF) was conducted on all samples. Advanced instruments such as DiamondViewTM laser Raman spectrometer, EXATM diamond tester and, FTIR spectrometer has also been usedfor the analysis. In conclusion, it is found that luminescence imaging and the PL spectrum are crucial in separating the CVD synthetic diamonds from their natural diamond counterparts

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Affiliation:

1. The Gem and Jewelry Institute of Thailand (GIT), Bangkok, 10500 Thailand
2. G-ID Laboratories, Bangkok, 10120 Thailand

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Conference Paper

Gemmological and chemical characteristics of Yiqisong peridot, Jilin, People Republic of China

Research Article

Conference Paper

36th International Gemmological Conference (IGC2019), Nantes, France

Gemmological and Chemical Characteristics of Yiqisong Peridot, Jilin, People Republic of China

By Tasnara Sripoonjan, Montira Seneewong Na Ayutthaya, Pimtida Bupparenoo, Nalin Narudeesombat, Thanong Leelawatanasuk, and Malin Sawatekitithum

2019, August 29

Figure 1: Representative samples of Yiqisong peridot from China ranging in weight from
1.60 to 2.80 ct (Photograph by T. Sripoonjan)

Abstract
China has traditionally been a territory of a great conundrum with a diversity of natural resources including minerals and gems, and especially green colored stones (e.g. jade, prehnite and peridot). Peridot has been found in a number of different areas of China. Since 1979, China has mined the peridot from the Zhangjiakou-Xuanhua area of Hebei Province (Koivula and Fryer, 1986; Keller and Fuquan, 1986). Recently, the significant deposit of gem-quality peridot has been found in the area called Yiqisong, Yanbian of Jilin province. At first glance, these peridots strikingly show a medium toned yellowish green attribute with high clarity. The average size of relatively clean stones was up to 2 ct. This article describes their detailed gemological characteristics, namely, basic properties, internal features, absorption spectra and chemical compositions.
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Affiliation:

1. The Gem and Jewelry Institute of Thailand (GIT), Bangkok, 10500 Thailand
2. College of Creative Industry, Srinakarinwirot University, Bangkok, 10110 Thailand

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