ISG Gemology Tools and Techniques - · PDF fileInternational School of Gemology Tools and...

ISG Gemology Tools and Techniques

Lesson Sixteen: Advanced Testing Tools

International School of Gemology Tools and Techniques Course

Introduction

With an increase in the sophistication of interpretation software, the use ofadvanced technology is quickly becomingan important tool for gemologists at alllevels of the industry.Previously, the use of Raman scans or FTIRwere considered out of the reach of the basicgemological lab due to the cost of theequipment and the need

for advanced training and education to be able to interpret the results.Recent developments in lower production costs and user friendly softwareinterpretation advancements, however, have made these advanced toolsboth affordable and viable for the grass roots level gemologist.


The scope of this lesson is to acquaint you with these various instruments that areeither 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 youaware 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 anymajor gemological school until this course. Indeed, when first presented to somesegments of the gemological industry the concept of gemstones being magnetic wastreated 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 thetreated or created versions give the opposite reaction to the natural.


At left is a picture of a parcel of garnetswith the almandite garnets beingstrongly magnetic to the point that amagnet will actually pick them up. This allows for separation of these naturalgarnets from other garnets and garnetimitations.


One method to demonstrate magnetism is by use ofa copper wire with a loop to hold the stone, andhung by a string. It is important to use a wire that isnon-magnetic.


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 magnetwill have with the garnet. By sliding the magnetsideway toward the gemstone it will eventually pullthe stone to the magnet. At the point that the

magnet and gemstone come into contact, the point on the scale can be marked forfuture reference. This is just one method to be able to quantify the magnetism for a gemstone.


The importance of this method can be demonstrated using color infused tourmaline. Atleft you see a natural pink tourmaline crystal withlittle or no magnetic reaction. As you will note atleft, 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 areaction in this testing set up.


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


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 wehave found that shows diamagnetism is the blue feldspar found in Kenya. We willtake a few minutes to demonstrate magnetic gemstones next.


Raman Technology

The Raman scan is a unique test based on the unique scattering of a laser beam whenit 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 causethe 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 foundto 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, allowsfor the identification of a material based on the software interpretation of thatscattering.


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


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


Here at left is a diamond that has beenirradiated, or radiation treated tochange the color. In this case theradiation has damaged the crystalstructure of the diamond, causing thescattering 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.


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 knownmaterials that have been tested and catalogued in a database, it is possible to identifyunknown materials by comparison. Below left is a Raman scan of a known cubiczirconia. Below right is a Raman scan of one of the Diamond Nexus Labs gemstonesthat 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 specificgravity, was able to verify the true identity of the Diamond Nexus Lab material assimple cubic zirconia.


As prices continue to fall for the Raman units, and software interpretation technologycontinues to advance, the use of the Raman for gemological applications will continueto expand throughout the industry. This important identification tool is already at aprice that is affordable to many working gemological labs, and the future holds greatpromise for the expanded use in the future.


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


UV-VIS-NIR Spectroscope

The most important feature of thisspectrometer is that the spectrum is visibleon a LCD television screen. Although the human eye cannot discern colors beyondthe visible spectrum, the MDM

Spectrometer transforms the absorptionlines into black and white images, allowingthe viewing of the full spectrum available.At left you see the full unit with screenshowing an absorption band of tanzanite.


At left is the portion of the visiblespectrum of irradiated amber which is unique due to the radiation treatmentof the material.

The display can be adjusted for intensity to make even the very faint absorption linesvisible.


At left you see a comparison of thevisible spectrum using a diffractiongrating spectroscope and the UV-VIS-NIR spectrum as seen through theMDM 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 diffractiongrating spectroscope (below in color) and the UV-VIS-NIR spectrometer (above inblack 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-NIRwill 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 spectrumof the UV and NIR visible, this allows us to see into areas were we do not see colors.


No one knows or can even dream of what the colors look like below 400nm or above700nm, but with this particular UV-VIS-NIR we can indeed “see” into these regions, ifonly in black and white.

Below is a wide-screen shot of the full UV-VIS-NIR spectrum with an overlay of thevisible 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 graphdisplay based on peaks and valleys. But this unit will actually allow the human eye tosee the full spectrum of this unit.


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


LA-ICP-MS

Laser Ablation Inductively Coupled Plasma Mass Spectroscopy is a very long namefor a rather straight forward advanced testing method. The LA-ICP-MS test uses alaser 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 theplasma vapor. This method of testing is very accurate and can identify elements downto the parts per billion. Although this testing method is fairly expensive, aroundUS$850.00 per scan at the time of this writing, it is the most accurate methodavailable to grass roots gemologists for elemental analysis of gemstone materials. Itshould be noted that it will be rare for a main stream gemologist appraiser to needthis level of advanced testing, but in the event that a full elemental analysis isrequired you should be aware of the test and what it will do for you.



At left you see a report from our investigations of the color infusedtourmaline where we proved the increasein iron and manganese by use of LA-ICP-MSfrom Evans Analytical Group Labs. You cansee that the elemental list is quite simple toread and understand. All one needs is a baseline of normal elemental composition of agemstone to be able to compare and identifyanomalies in the report. In this case the Mnand Fe are astronomically high, providingstrong evidence that some type of artificialinfusion of elements was done to thistourmaline. By this method we were able toconfirm the color infusion of tourmaline.

X-ray Fluorescence is a very important type of elemental analysis that was also widelyused by the ISG for both the tourmaline investigations and the Tibet andesine fraudexposure. Like the LA-ICP-MS analysis, XRF is an elemental analysis method but it isnot as complete or as expensive as LA-ICP-MS. XRF uses an X-ray beam to impact asmall part of the material being testing, then uses a mass analyzer to identifyelements within the material. XRF does not have the complete elemental reach ofLA-ICP-MS as it has a limited number of elements it can identify based on a number offactors 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 elementscan be narrowed down for the search and the XRF unit adjusted to look for thosespecific elements.


XRF

Rather than giving a parts per billion type of report the XRF will normally provide a Concentration in Weight-% report. Thismeans that a weighted report is generatedshowing 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 thesuspected color infused tourmaline fromMadagascar. 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 readingswere almost double in Mn and Cu. Since the


infusion of materials into a gemstone causes a significant increase in elements in theinterior 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 cutand 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 ofthis color treatment being done on the other tourmalines to try to emulate the trueand natural Paraiba tourmalines. The XRF is a very important and cost effectivemethod to identify elements in a gemstone if that level of testing is required.


SEM EDXS

Scanning Electron Microscope Energy Dispersive X-ray Spectroscopy: AnotherHUGE name for a very important and cost effective advanced testing methodavailable now to gemologists.

With this method a scanning electron microscope is used to direct x-rays into amaterial and use a very advanced spectroscope to identify the elements in thematerial. In the case of the SEM, variable intensities of the x-ray can be set tospecifically identify certain elements.


The graph below is the actual report from FAI Materials Testing on the Tibet andesine supplied by the Hughes/Schorr Tibet andesine expedition. This materialwas 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, whichwas not something that one would naturally find on basaltic type feldspar that wasall natural and had been in an alluvial fan for millions of years. In truth, sulfur is amajor ingredient in graphite/sulfur crucibles used in China to artificially treatgemstones. As confirmed by the National Gem Testing Center of China, these Tibetandesine were actually artificially colored by treatment and not natural. By SEM wewere able to identify a relic of the treatment crucible that led to the confirmation ofthe situation.


The Tibet andesine expeditions were either the victims of a very elaborate hoax asreported by several others, or they were perhaps perpetrators who were in on thescam. Either way, the specimens provided by the expeditions have proven to betreated and not natural as claimed. The SEM EDXS was crucial for this purpose.

Perhaps most important is that SEM EDXS testing is relatively inexpensive whencompared to other testing. At the time of this writing we could get four scans done by FAI Materials Testing for around US$300.00 per hour with a two hour timerequirement. So the testing is very accurate for elemental analysis and very costeffective.


FTIR

Fourier Transform Infra-Red Spectroscopy is the name of this important testing usedto identify and separate natural amethyst and other quartz gemstones from the hydrothermal lab-created specimens out on the market. The separation ofhydrothermal quartz from natural quartz is very difficult without FTIR; in fact it isvirtually impossible unless the gemologist is fortunate enough to find particular typesof inclusions that are covered elsewhere in our course program. FTIR testing isrelatively inexpensive by independent labs, although trying to own one can beexpensive for the starting gemologist since they currently cost around US$25,000.00. 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 doother testing that is available by FTIR, there are alternatives to having to own one.


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 tocontinually research these testing methods to know what is available and what is about to become available. As the gemstone “cookers” develop new treatments it willbe important for you to stay informed of the various methods available to you toidentify these. It is an ongoing study that you should always devote a certain amountof 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 FinalExam. Return to the course home page to take your Final Exam.

©2015 International School of Gemology. ALL RIGHTS RESERVED. No copying, duplication or distribution of these course notes is allowed.


ISG Gemology Tools and Techniques - · PDF fileInternational School of Gemology Tools and...

Documents

Transcript of ISG Gemology Tools and Techniques - · PDF fileInternational School of Gemology Tools and...