Back to IGS | FAQ | Contact

IGS Practical Exam


#1

Hi guys,

Just wondering if anyone had any hints for identifying the stones sent out for the IGS Practical Exam? I am light on for equipment so any list of identification equipment needed would also help…

Thanks in advance :+1:


#2

Hi!
You will certainly need a precision scale with some specific gravity kit, a good refractometer, a dichroscope, a UV lamp (SW/LW) and a gemological microscope (or at least, a convencional one with some darkfield adaptation). There is no way to do an accurate work without that.

Have a look at this guys, they have a lot of stuff: http://www.kassoy.com/prodcat/Gemological-Equipment.asp
:vulcan:


#3

My advice goes against what many people would tell you about traditional gemology. If you have less equipment, you need more knowledge. It is relatively easy to use a refractometer and once you have an RI and perhaps a birefringence (if doubly refractive), a couple of confirmatory tests usually does it. Think refractometer, dichroscope, some kind of magnification, maybe a UV lamp and diffraction grating spectroscope. An inexpensive chinese refractometer should work OK…but get a return privilege and check it with a piece of quartz, which is pretty invariant and make sure it reads correctly.

You can also use a scheme which depends on SG rather than RI as a starting point. An electronic scale and a small cup of water in a little plastic salad dressing cup along with some fishing line allows you to take a weight by laying the stone down on the bottom of the water filled cup and immersed weight by lifting it off the bottom (using the tare function). Very simple and no complicated shelf for a beaker, etc. Then if you have a polariscope and a strainless sphere and a quartz wedge substitute, you can determine SG, and optic character and optic sign. These pieces of data, along with an examination with magnification, should allow you to ID about any transparent gem and most opaque ones. Polariscopes can be built from plastic polaroid sheet material or from two old photo filters…find a night light or flashlight. There are also pocket polariscopes based on a flashlight on ebay. The strainless sphere is an acrylic ball and the wedge substitute is the side of a lucite box. If you read Hanneman’s Affordable Gemology he covers all of this as well as gemology without instruments (aka Visual Optics). It’s a good use of $50.

These days, with cheap instruments from China, you could get a refractometer for $100 or so and the other instruments you need for $100 to $300 more and get on with it. But the contrarian in me has to say that you could use a $30 scale and a $30 flashlight polariscope along with a good LED lighted loupe ($20) and a dichroscope ($27) and visual optics and be done. I’d get a UV laser just because they are cheap and so much fun and add a standard magnet ($15??) for magnetism tests, which are also cheap, quick and helpful. About $130, maybe less if you shop well on ebay or already have a loupe or scale. Things were a lot different back before ebay and chinese imports of refractometers, microscopes, etc. Then we were looking at at least $1000 and that was somehow finding and buying used. If you bought from the GIA store, you were looking at $3000+.

Of course, if you are IDing mounted stones, the refractometer is most useful, esp. if the mounting keeps you from turning the stone under the polariscope well. At any rate, get Hanneman’s book if you are serious about gemology…there is stuff in there you won’t find elsewhere.
Hope this helps,
Royjohn


#4

Hi I tried the practical with just a 20 x Loupe and could get 11 of the 15 questions correct but the he last 4 is difficult and have taken the exam twice. I will have to get extra equipment to pass the exam. Good luck. There is good advice here about the necessary equipment