Many Hats of Me: Gemology instruments

Thursday, January 17, 2013

Gemology instruments

It started with a stone

I became interested in gems and gemology when my sister announced that she was getting married. In my culture, giving jewelry to the relative who is getting married is customary. During my endless  Google searches, I found a website that sold gemstones from Thailand called Gemselect. This website sells loose gemstones that are offered at fair to high prices. I was really intrigued and called the owner, who is an American living in Thailand. He was very helpful and I decided to buy some stones from him. I purchased a large green tourmaline, and pairs of smaller gemstones that are sized to fit in standard rings.


Dark Green Tourmaline


3.1 karat Green Tourmaline
(destined to be set in an Argentium silver ring, for my sister's finger +Lesley Phord-Toy )


After a year of collecting over a hundred stones from different suppliers, I am finally ready to purchase gem testing equipment.

I began surfing the web and came across a very helpful site called Gemology Online. Here, you can post a question in the "beginner" section and an expert will answer if they can. Searching topics in their older posts are also the way to go to find info about gems and gemology.

From here, I learned about some of the basic gem testing equipment:



must have gemology instruments

A good LED penlight, a halogen Mag-lite, polymer clay, Jadeite or Chelsea filter, a spectrometer, dichroscope, polariscope (not shown), a shortwave UV light, and a microfiber cloth.


Jadeite Filter

A Jadeite or Chelsea filter is one of the most basic tests. You hold your stone under a strong halogen light and look at it through this filter. The stone's color seen through the filter will provide some information about the stone. It is the simplest test to perform, but the results are not conclusive.


Polymer clay cuts down the light so that it only shines through a gem



The polymer clay is used to hold a stone in position while photographing and also to create a donut shape on top of your halogen Maglite (LED spectrum is inappropriate for gem ID) to close off all light except the middle where you will place your stone. 




Tsavorite stone on top of Fimo clay

You view the light coming through the gem with a spectroscope to see the stone's light absorption patterns. To ID stones, you compare your stone to a known pattern of stone, as can be found in the online gem database Geminterest. I find it very difficult to see patterns clearly and quite honestly, I can't recommend this instrument to gemology newbies. 


rhodolite gem spectrum as seen through a spectrometer

Here is the spectral pattern of a rhodolite garnet I photographed through the spectroscope


A spectroscope is used to see the color absorption pattern in gemstones. 

A dichroscope is used to see pleochroism in colored stones, which is the stones ability to split light into different colors. By referencing a gem database, you may narrow down the ID of your stone.

A polariscope shows if a stone is singly or doubly refractive. If it's singly refractive, your stone will stay dark as you turn the polarizer; if it's doubly refractive, it goes from light to dark when you turn the polarizer. I recommend this device since it's really easy to use for a beginner.

UV light, both long wave, and short wave, can help ID certain gems, such as rubies and diamonds, that have a reaction to this type of light.

A microfiber cloth is necessary to remove dust, dirt and oil from your gem before observation. They are about $7 to $10+, but I bought mine at Costco where for $25, I got 36. 


polariscope



Have I lost you yet? As you can see, there are many tests to perform when ID'ing stones. The above tests are ones that utilize instruments that are not expensive to purchase, unless you buy top of the line, such as my British-made OPI spectrometer and dichroscope from England. All can be purchased via Ebay or Amazon. 

The two instruments that professional gemologists use primarily are the stereo microscope and the refractometer. They are very expensive to purchase, and thus I am just starting to put together my microscope, one piece at a time through individual purchases from science lab resellers, such as Labx and BMI surplus, and of course, eBay. 

A refractometer measures a stone's refractive index, which is the way a stone internally reflects light. A stone's RI measurement paired with a careful examination under a microscope can provide a positive ID if performed by an experienced person. The other tests mentioned earlier just confirm their conclusions.

My holy grail is a used genuine GIA refractometer. I look daily on eBay for this important gemological instrument. It retails for $925! Also keep a look out British-made Rayner refractometers.

GIA Gem Refractometer


If you are interested in learning more about gemology, I highly recommend Professor Barbara Smigel's free gemology course that is a gemology primer. It's easy to understand and a fun read and will start you on your path to gem knowledge!













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