GemSelect Newsletter - October 2009
The task of gem identification is often quite straightforward, and can be competently handled by any knowledgeable gemologist using standard instruments that measure properties such as refractive index and specific gravity. But there are cases that are not so straightforward, and require need help from a laboratory with state-of-the-art equipment and experienced staff.
In the past we've provided gemstone certification from the local lab here in Chanthaburi, the Burapha Gemological Laboratory (BGL). They are a competent and ethical lab, and provide an efficient and cost-effective service for the busy gemstone market here.
But the local lab is not able to test every kind of stone and identify every kind of treatment. Since we sell more than 110 different gem varieties and many kinds of untreated stones, we found ourselves sending more and more gems to Bangkok for testing. After trying a number of different labs, we found a lab that could reliably certify virtually every kind of stone: The Asian Institute of Gemological Sciences, widely known as AIGS.
There are a number of cases which require advanced instruments and special expertise to certify a gemstone. The most frequent case we encounter is that of unheated sapphires. Unheated sapphires are identified by the presence of characteristic inclusions that would be altered by heat treatment. But it takes considerable knowledge and experience to recognize these inclusions. The AIGS gemologists have many years of experience in analysing sapphire, and each gem is checked by two gemologists before a certificate is approved. If the experts are not 100% confident of their conclusions, a certificate will not be issued.
Quartz is another difficult case. Although quartz is one of the most common minerals in the world, distinguishing natural from synthetic quartz is a challenge, especially when it comes to very clean specimens. Many gem labs will simply issue an "undetermined" verdict when analysing a quartz sample, since they don't have the expertise to reliably identify synthetic material. AIGS is able to perform an analysis using infrared spectroscopy, in addition to microscopic analysis of inclusions and twinning.
We had another case recently where we had some black gemstones that the local lab could not identify. Based on the measurements of refractive index and specific gravity, they thought it could be garnet. We sent samples to AIGS, who were able to identify it conclusively as black spinel. Even though the refractive index seemed to be out of the normal range for spinel, analysis of the chemical composition using an EDXRF (Energy Dispersive X- Ray Fluorescence) spectrometer showed conclusively that it was an iron-rich spinel.
We use AIGS to test samples of all new gems we buy, and for testing rare or unusual gems such as the padparadscha sapphire featured in this month's newsletter. We will soon begin offering some pre-certified gems, for which the certificates will be shown online.
Each month we feature a rare and unusual gem from our inventory. This month we feature a very rare unheated padparadscha sapphire from Tanzania:
The rarest and most valuable color in sapphire is called padparadscha. The name is said to be derived from the Sinhalese term for lotus flower. The color is subtle, but the rule is that a true padparadscha sapphire must display both orange and pink hues with a pastel tone. Since the elusive color is so rare, sapphires that display this color without the help of any treatment are especially prized. In fact, many connoisseurs would argue that a true padparadscha must always be untreated.
This 0.51 carat, orange-pink sapphire from Tanzania has been certified by AIGS as an unheated padparadscha sapphire. It is a stunning gem, with a delicate balance of orange and pink. It is also very clean and we've graded it VS (almost loupe clean). This is truly a rare stone.
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Happy Gem Hunting!
Your friends at GemSelect
- First Published: October-01-2009
- Last Updated: June-29-2017
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