ISG Gemology Tools and Techniques

Transcription

1 ISG Gemology Tools and Techniques Lesson Sixteen: Advanced Testing Tools

2 Introduction With an increase in the sophistication of interpretation software, the use of advanced technology is quickly becoming an important tool for gemologists at all levels of the industry. Previously, the use of Raman scans or FTIR were considered out of the reach of the basic gemological lab due to the cost of the equipment and the need for advanced training and education to be able to interpret the results. Recent developments in lower production costs and user friendly software interpretation advancements, however, have made these advanced tools both affordable and viable for the grass roots level gemologist.

3 The scope of this lesson is to acquaint you with these various instruments that are either now or will soon be available to you at cost effective prices. While a full technical training program is outside the scope of this course, we want to make you aware of these tools and the potential benefits that they provide. Magnetism This is not a new gemological testing tool, although it has not been taught by any major gemological school until this course. Indeed, when first presented to some segments of the gemological industry the concept of gemstones being magnetic was treated as absurd. But the truth is that due to magnetic metals being a part of many gemstones, these gemstones do provide specific reactions to a magnet. With other gemstones it has been found that lab created and treated versions can be identified due to the fact that natural gemstones may or may not be magnetic, while the treated or created versions give the opposite reaction to the natural.

4 At left is a picture of a parcel of garnets with the almandite garnets being strongly magnetic to the point that a magnet will actually pick them up. This allows for separation of these natural garnets from other garnets and garnet imitations.

5 One method to demonstrate magnetism is by use of a copper wire with a loop to hold the stone, and hung by a string. It is important to use a wire that is non-magnetic.

6 As you can see in the image at far left, we can print a series of lines on a paper to serve as a demonstration scale of how much pull the magnet will have with the garnet. By sliding the magnet sideway toward the gemstone it will eventually pull the stone to the magnet. At the point that the magnet and gemstone come into contact, the point on the scale can be marked for future reference. This is just one method to be able to quantify the magnetism for a gemstone.

7 The importance of this method can be demonstrated using color infused tourmaline. At left you see a natural pink tourmaline crystal with little or no magnetic reaction. As you will note at left, the wire has not moved from the scale and the gemstone crystal is not touching the magnet. This demonstrates that pink tourmalines are not naturally magnetic to an extent that causes a reaction in this testing set up.

8 Below, however, is a tourmaline that has been artificially treated for color using a method that uses iron in some manner or method. While the specific treatment method is unknown, the results are easily identifiable using a magnet. Below left is the pink tourmaline rough with the wire needle pointing straight down. Below right is the same pink tourmaline with the magnet to the side. This pink tourmaline is so strongly magnetic that it is pulled to the edge of the reading scale. Since we know that natural pink tourmaline is not magnetic, the strong magnetism of this rough crystal demonstrates that some artificial process has been done to this tourmaline rough crystal. This is but one example of how magnetism can be used to help identify both the gemstone and potential treatments.

9 Diamagnetic While most gemstones will attract a magnet, some will repel the magnet. This property is known as diamagnetism. One of the more notable natural gemstones we have found that shows diamagnetism is the blue feldspar found in Kenya. We will take a few minutes to demonstrate magnetic gemstones next.

10 Raman Technology The Raman scan is a unique test based on the unique scattering of a laser beam when it strikes a gemstone s surface. This is known as Raleigh Scattering and is the basis for the Raman scan. When a laser beam is directed to a material, the material will cause the laser beam to scatter in a unique pattern based on many factors that, once again, go beyond the scope of this course. But the unique scattering of the laser was found to be a method to identify certain gemstones. The Raman is not an elemental analysis, meaning it cannot identify what elements comprise a particular gemstone. Instead, the unique scattering of the laser beam, based on the Raman interpretation, allows for the identification of a material based on the software interpretation of that scattering.

11 At left is a Raman Microscope made by the Enwave company and owned by the ISG. This Raman unit was custom built on a Meiji Techno microscope to allow scans to be done on microscopic level materials. This allows materials on the surface of a gemstone to be scanned and identified by use of a much smaller target area to being tested.

12 At left is a scan of a natural, untreated diamond. You can see the single peak at around 1332nm (nanometer). This is a classic and diagnostic Raman scan of a natural, untreated diamond.

13 Here at left is a diamond that has been irradiated, or radiation treated to change the color. In this case the radiation has damaged the crystal structure of the diamond, causing the scattering of the laser to alter. This hump you see in this image is referred to as Raman photoluminescence and is also diagnostic for diamonds that have been treated with radiation to alter their color. By use of Raman technology it is possible for a gemologist to positively identify a yellow diamond has being natural or having been subjected to radiation to achieve the color.

14 The use of the Raman and Raman photoluminescence is a fast growing technological advancement in the world of gemology. As you can see below, by comparing known materials that have been tested and catalogued in a database, it is possible to identify unknown materials by comparison. Below left is a Raman scan of a known cubic zirconia. Below right is a Raman scan of one of the Diamond Nexus Labs gemstones that are claimed to be either a lab created diamond or some type of gemstone hybrid. As you can see below, the DNL material tests identical to the known cubic zirconia. This test, along with confirmation testing done using refractive index and specific gravity, was able to verify the true identity of the Diamond Nexus Lab material as simple cubic zirconia.

15 As prices continue to fall for the Raman units, and software interpretation technology continues to advance, the use of the Raman for gemological applications will continue to expand throughout the industry. This important identification tool is already at a price that is affordable to many working gemological labs, and the future holds great promise for the expanded use in the future.

16 UV-VIS-NIR Spectroscope These initials stand for ultra-violet, visible and near infrared; or put another way, they describe the wavelengths of light that can be utilized by the UV-VIS-NIR Spectroscope. This is a unique technology as it extends the ability of the spectroscope well beyond the visible spectrum and takes it into the ultra violet to a small degree, and the near infrared to a greater degree. At left you see the spectroscope unit of the MDM Spectrometer at the ISG office, made by Imperial Instruments.

17 The most important feature of this spectrometer is that the spectrum is visible on a LCD television screen. Although the human eye cannot discern colors beyond the visible spectrum, the MDM Spectrometer transforms the absorption lines into black and white images, allowing the viewing of the full spectrum available. At left you see the full unit with screen showing an absorption band of tanzanite.

18 At left is the portion of the visible spectrum of irradiated amber which is unique due to the radiation treatment of the material. The display can be adjusted for intensity to make even the very faint absorption lines visible.

19 At left you see a comparison of the visible spectrum using a diffraction grating spectroscope and the UV-VIS- NIR spectrum as seen through the MDM Spectrometer. This specimen is a YAG used to calibrate the spectrometer. You can see in this comparison image the absorption lines match up nicely between the colors of the visible spectrum as seen through a diffraction grating spectroscope (below in color) and the UV-VIS-NIR spectrometer (above in black and white). You can see how the absorption lines match up demonstrating the accuracy of the UV-VIS-NIR. Here is where it gets interesting. As you have probably surmised, if the UV-VIS-NIR will display beyond the visible spectrum, then this is an opportunity to be able to see into areas of the spectrum never before seen. Indeed, by making the spectrum of the UV and NIR visible, this allows us to see into areas were we do not see colors.

20 No one knows or can even dream of what the colors look like below 400nm or above 700nm, but with this particular UV-VIS-NIR we can indeed see into these regions, if only in black and white. Below is a wide-screen shot of the full UV-VIS-NIR spectrum with an overlay of the visible spectrum of the diffraction grating spectroscope. This is dramatic proof of just how amazing this spectrometer is by allowing a visible image of the complete UV- VIS- NIR spectrum that this unit can produce. Most UV-VIS-NIR spectrometers use a graph display based on peaks and valleys. But this unit will actually allow the human eye to see the full spectrum of this unit.

21 Obviously, the expanded reach of UV-VIS-NIR technology serves to provide a far more in-depth evaluation of a gemstone's identification. Since the width of the spectrum is extended, the number of verifiable absorption lines and bands is also expanded allowing for greater accuracy in gem identification. As this technology improves and the prices of the spectrometers continue to go down, the viability of this spectrometer will allow it to be available to more and more grass roots gemologists.

22 LA-ICP-MS Laser Ablation Inductively Coupled Plasma Mass Spectroscopy is a very long name for a rather straight forward advanced testing method. The LA-ICP-MS test uses a laser to ablate (or in this case vaporize) a small amount of the material being tested. A very advanced type of mass analyzer is then used to identify the elements in the plasma vapor. This method of testing is very accurate and can identify elements down to the parts per billion. Although this testing method is fairly expensive, around US$ per scan at the time of this writing, it is the most accurate method available to grass roots gemologists for elemental analysis of gemstone materials. It should be noted that it will be rare for a main stream gemologist appraiser to need this level of advanced testing, but in the event that a full elemental analysis is required you should be aware of the test and what it will do for you.

23 At left you see a report from our investigations of the color infused tourmaline where we proved the increase in iron and manganese by use of LA-ICP-MS from Evans Analytical Group Labs. You can see that the elemental list is quite simple to read and understand. All one needs is a base line of normal elemental composition of a gemstone to be able to compare and identify anomalies in the report. In this case the Mn and Fe are astronomically high, providing strong evidence that some type of artificial infusion of elements was done to this tourmaline. By this method we were able to confirm the color infusion of tourmaline.

24 XRF X-ray Fluorescence is a very important type of elemental analysis that was also widely used by the ISG for both the tourmaline investigations and the Tibet andesine fraud exposure. Like the LA-ICP-MS analysis, XRF is an elemental analysis method but it is not as complete or as expensive as LA-ICP-MS. XRF uses an X-ray beam to impact a small part of the material being testing, then uses a mass analyzer to identify elements within the material. XRF does not have the complete elemental reach of LA-ICP-MS as it has a limited number of elements it can identify based on a number of factors that are beyond the scope of this course. However, since the cost of XRF is far less than LA-ICP-MS it can be a very important alternative when specific elements can be narrowed down for the search and the XRF unit adjusted to look for those specific elements.

25 Rather than giving a parts per billion type of report the XRF will normally provide a Concentration in Weight-% report. This means that a weighted report is generated showing the percentage of the elements in the material tested. At left is a XRF report done for the ISG, also by the EAG Labs. This was in regards to the question of true Paraiba tourmaline and the suspected color infused tourmaline from Madagascar. If you compare 2-Interior and Exterior you will see that the elemental percentages are nearly identical. In 3-Interior and Exterior, however, the Interior readings were almost double in Mn and Cu. Since the

26 infusion of materials into a gemstone causes a significant increase in elements in the interior of the gemstone, it was anticipated that if the Mozambique tourmaline had been color infused we would find a spike of Mn and Cu inside the gemstones once cut and tested inside. This XRF report above was used to further confirm the previous LA- ICP-MS testing of the Mozambique material that eventually led to the exposure of this color treatment being done on the other tourmalines to try to emulate the true and natural Paraiba tourmalines. The XRF is a very important and cost effective method to identify elements in a gemstone if that level of testing is required.

27 SEM EDXS Scanning Electron Microscope Energy Dispersive X-ray Spectroscopy: Another HUGE name for a very important and cost effective advanced testing method available now to gemologists. With this method a scanning electron microscope is used to direct x-rays into a material and use a very advanced spectroscope to identify the elements in the material. In the case of the SEM, variable intensities of the x-ray can be set to specifically identify certain elements.

28 The graph below is the actual report from FAI Materials Testing on the Tibet andesine supplied by the Hughes/Schorr Tibet andesine expedition. This material was reported to be all natural and untreated by the expedition members. However, by SEM we were able to identify the presence of sulfur (S) on the specimens, which was not something that one would naturally find on basaltic type feldspar that was all natural and had been in an alluvial fan for millions of years. In truth, sulfur is a major ingredient in graphite/sulfur crucibles used in China to artificially treat gemstones. As confirmed by the National Gem Testing Center of China, these Tibet andesine were actually artificially colored by treatment and not natural. By SEM we were able to identify a relic of the treatment crucible that led to the confirmation of the situation.

29 The Tibet andesine expeditions were either the victims of a very elaborate hoax as reported by several others, or they were perhaps perpetrators who were in on the scam. Either way, the specimens provided by the expeditions have proven to be treated and not natural as claimed. The SEM EDXS was crucial for this purpose. Perhaps most important is that SEM EDXS testing is relatively inexpensive when compared to other testing. At the time of this writing we could get four scans done by FAI Materials Testing for around US$ per hour with a two hour time requirement. So the testing is very accurate for elemental analysis and very cost effective.

30 FTIR Fourier Transform Infra-Red Spectroscopy is the name of this important testing used to identify and separate natural amethyst and other quartz gemstones from the hydrothermal lab-created specimens out on the market. The separation of hydrothermal quartz from natural quartz is very difficult without FTIR; in fact it is virtually impossible unless the gemologist is fortunate enough to find particular types of inclusions that are covered elsewhere in our course program. FTIR testing is relatively inexpensive by independent labs, although trying to own one can be expensive for the starting gemologist since they currently cost around US$25, But since there are plenty of independent testing labs available on the market who provide FTIR testing, in the event that you need to confirm a large amethyst or do other testing that is available by FTIR, there are alternatives to having to own one.

31 There are a variety of other tests that are either available or will soon be available to the grass roots gemologists at cost effective prices. It will be important for you to continually research these testing methods to know what is available and what is about to become available. As the gemstone cookers develop new treatments it will be important for you to stay informed of the various methods available to you to identify these. It is an ongoing study that you should always devote a certain amount of your market research on to be able to keep yourself and your clients well informed. This is the end of Lesson Sixteen: Advanced Testing Tools. It s time to take your Final Exam. Return to the course home page to take your Final Exam International School of Gemology. ALL RIGHTS RESERVED. No copying, duplication or distribution of these course notes is allowed.