Tools of the Gemologist

by Donald Clark CSM

Gemology involves studying the physical and optical properties that make gems such unique little treasures. As one graduates into gem identification, it is these physical and optical properties that distinguish one species from another. When setting up a gem lab, a number of instruments are used to distinguish or measure these properties. First though, you need good reference books to make sense of what the instruments tell you.

All the information you need can be found in the IGS Reference Library, but you may want other books in your library. Highly recommended is Gemology Tools. This is a new piece of software that makes gem identification much easier than ever before. We have an article titled Modern Determinative Gemology that details a new method of gem identification based on Gemology Tools. With it, both the time spent identifying gems and the chance of errors is greatly reduced. You can get a copy of Gemology Tools at a substantial discount with your membership.

The most complete book written is the Color Encyclopedia of Gems by Dr. Joel Arem. It lists approximately 3,000 minerals and man made materials that have been cut as gems. It is now out of print, but it is worth tracking down a used copy.  Fortunately for us, Dr. Arem has generously allowed the IGS to re-print much of the information from his out of print book in various places on this website, and where we have done so we have indicated him as the source.

While the Color Encyclopedia of Gems is the most comprehensive, beginners might want to start with something simpler. Another excellent book is Gemstones of the World by Walter Schumann. It reads a bit easier and has more information about peripheral subjects like gem sources. It also cost about half as much as the encyclopedia does. This was originally written over 20 years ago and some of the information is now dated. If you look for a copy, make sure it is a recent edition.

Two other excellent reference books are available from the GIA, (Gemological Institute of America.) The Gem Reference Guide is similar to the Color Encyclopedia of Gems. In some ways it is easier to read and use, but it has the major disadvantage that it only deals with the hundred or so stones that are “most likely” to show up in jewelry.

Their Handbook of Gem Identification describes in detail how to use the tools of the gemologist. It also gives step by step instructions on separating the species. This is unquestionably one of the best books ever written on gem identification, however the modern method using Gemology Tools is much easier.

From Europe is Gems, Their Sources, Descriptions and Identification by Webster and Anderson. This is also an excellent reference work, based on traditional methods of gem identification. However, a word of caution is in order. New, this book is about $60. Occasionally you will find it with a special price of about half that amount. These discounted books are old versions that contain quite a bit less information that the current edition.

Once you have your reference books together, you can begin assembling your lab equipment. At the top of the list is magnification. Begin with a good quality, ten power loupe. There are some economy loupes on the market that range from mediocre to very good quality. The best you can get, and the standard for diamond grading, is a color corrected, triplex loupe. Triplex means there are three lenses in it, so there is no distortion near the edges. Color corrected refers to a coating on the lenses so the color you see is accurate.

You are also going to need a microscope for studying inclusions. This is often the only way to separate natural gems from their synthetic counterparts. While the loupe is more portable, the microscope is easier on the eyes and offers higher magnification.

A gem microscope has special features that aren’t available on most microscopes. Make sure you get a sterio microscope. A standard, single tube microscope is almost useless. You need a minimum of 40 power for your identification, but more is certainly helpful. With higher magnification you will be able to see more inclusions and see them with greater detail. The higher power will sometimes mean the difference between being able to make an identification or not.

Good quality microscopes can cost several thousand dollars. In the last few years some new ones have come on the market that are just a few hundred dollars. There are still less expensive ones that can be adapted to gemological use. As a general rule, you want as good quality instruments as you can afford, but in microscopes compromises can be made for the sake of budget without a significant sacrifice in quality.

You need to consider if your microscope is going to be in view of the public. If that isn’t a consideration, realize that a moderate priced microscope can be just as useful as a $5000 one. The bottom line is that the information gathered from a microscope has more to do with the skill of the operator than the quality of the optics.

A method to measure the refractive index of your gems is a high priority. This can be done with a microscope, but a refractrometer is the best tool. Besides the RI, a refractrometer will also give you the birefringence and optic sign. When possible, it is easier to obtain the optic sign from a polariscope. However, that can’t always be done, so you need the refractrometer as an alternate means to determine the optic sign when necessary.

Refractrometers costs in the neighborhood of $500 to $1000. In North America the primary source is the Gemological Institute of America. In Europe the primary supplier is Kneuss Instruments. Used refractomers occassionally come available on eBay.

Another gem lab necessity is a means to measure specific gravity. There are two methods for doing this, both of which are under $100. A balance beam scale can be used, provided one pan can be submerged in water. That is usually an easy thing to arrange. The other method is to use “heavy liquids.” These are a collection of liquids with predetermined specific gravity’s. You determine the specific gravity of a gem by submersing it in the liquids and observing how much it floats or sinks.

Heavy liquids have the disadvantages of being toxic and flammable, so a lot of care needs to be exercised when using them. Also, they are difficult to wash off the gem. Your readings will always be an estimate with the liquids. If you have an accurate scale, you can get a much more precise reading. There will be occasions when this is important, as a small fraction can sometimes confirm or eliminate a possible identification.

There are three articles describing specific gravity testing in our Reference Library. Scroll down to the “Practical Gemology” section to find them.

Next on the list is an inexpensive item called a dichroscope. This is a small, hand held instrument that separates the colors in dichroic materials. Its essential elements are two small pieces of polarizing material oriented at 90o to each other, plus magnification. With a little thought and skill, you can make one yourself.

Equally important and just a little more expensive is a polariscope. It is used with a thing called a strainless sphere, (that is a glass sphere with no strain lines in it,) or a loupe. These are used to determine if a material is singly or doubly refractive and its optic sign. It will also show strain and twinning, which will occasionally help to distinguish between natural and man made materials.

Polariscopes can be purchased or made at home. The primary requirements are an underneath light source and two pieces of polarizing material that are separated enough to hold a gem between them. One piece of polarizing material can be stationary, but the other needs to be rotated in place.

If you get serious about your gemology, and specifically gem identification, you are going to need a spectroscope. There are essentially two different kinds, defraction grating and prism. They both do equally well, but the scale is more elongated in the prism style. If you are relying on images in a reference book to help you determine what you are seeing, make sure they are of the same kind as your instrument. Otherwise the comparisons get very confusing.

Another feature that is important to look for is a calibrated scale. Most people learn to use one without a scale and make their determinations strictly by the colors. The ability to do this depends on your eyesight and experience. Until you have looked at enough gems, it will be difficult to make an accurate assessment.

A spectroscope with a calibrated scale is preferred to one without a scale. However, you will find that this adds tremendously to the price. This is something you need to weigh into your priorities.

Still other factors that adds to the price is lighting and a stand. You need both a bright light source and a means to hold the gem, spectroscope and light source steady while studying. If these are all built in it will be easier to use, but also more expensive. If you are handy with your hands, you can create these elements and save some money.

There are diffraction grating spectroscopes on the market for under $100. They are the most difficult spectroscopes to use. You must find a way to hold them very still in relationship to the gem and the light. To add to the complication, you focus a diffraction grating spectroscope by moving it closer and further from the gem. Since the display is much darker than a prism spectroscope, lighting is a particular consideration. (See our review of the GL Spectroscope Lite.)

The spectroscope is one of the last instruments you will need to add to your lab. It will take the most consideration if you have a budget to adhere to, (and who doesn’t?) Prices run into the thousands of dollars for top of the line instruments with all accessories. Look at getting the best instrument you can afford, then make your compromises on the lighting and stand.

The above represent the major, “must have” tools of a gem lab. Of course you will need to acquire a bunch of other odds and ends. You will need a gem cloth for cleaning your gems, or some kind of strainer so they don’t go down the drain if you clean them in the sink. To hold your gems you will need tweezers or a stone holder. Small glass dishes are used for immersion studies. A stone line, to lay your stones side by side and upright, is needed for grading. Calipers or a micrometer are also essential. A scale to weigh your stones isn’t a necessity for learning, but is a high priority for trade.

We haven’t discussed lighting, but that is something that needs careful consideration. Standard lights will suit the majority of your needs, but you will need something that is flexible and easily moved into useful positions. A flexible arm light, or even a good quality flashlight, will be a big asset in your studies. Specialty lights will either be built in to some of your instruments, or you will need to create them.

Bear in mind that incandescent and fluorescent will give you different colors in some gems. If at all possible use incandescent, (or a window,) as your primary light source. If the room you use as a lab has fluorescent lighting already installed in the ceiling, you will need to turn it off or shield it at times.

One of your most useful light sources is a window, one with indirect light. Filtered sunlight is the standard for comparison of colors. Also, do not make the mistake of thinking you can rely on daylight equivalent lights for color change comparisons. They work in many cases, but in others they don’t. More than one gemologist has been embarrassed by relying on artificial lights.

While not absolutely necessary, ultraviolet light is sometimes helpful in making an identification. You will need both long and short wave UV for testing. A low powered light is sufficient, but it will need to be mounted in a box that doesn’t allow any other light to enter.

A Chelsea Filter is also a very handy thing to have. It was originally called the “Emerald Filter” because it was used to separate emeralds from their look alikes. Since some emeralds get their coloring from vanadium, it does not work in all cases. Now we recognize that its primary use is to determine if a material gets its color from chromium. If it does, the stone will appear pink or red through the Chelsea filter. If not, you will see something else.

This is important because gems like chrome pyrope and chrome tourmaline have a different value structure than their counterparts. While you can make this determination with a spectroscope, a Chelsea filter is the easiest way to distinguish these gems. There are other filters that are of some value, but none are as useful as the Chelsea filter.

There is a new instrument on the market called the Jewelers Eye that measures luster. It was designed for the traveling professional. This is not for the beginner, but for the knowledgeable gemologist who needs a portable instrument.

If your work requires you to identify small stones in settings, a diamond detector becomes a necessity. Small, low quality, dirty diamonds are impossible to distinguish by eye.

Hardness points, pencil like things with ends made of varying materials, are one of the standard tools of the mineralogist. They are used for determining the hardness of a substance. If you are going to be identifying rough, you might want to include these in your lab. You should NEVER use them on a cut gem. At the least, it leave a permanent scratch and it could cause the gem to break. If you are using it on rough, make sure you test a small area that is separate from the cuttable portion of the rough. Stress on cleavage planes can cause the stone to split in two!

Streak testing is another tool of the mineralogist. All it requires is a small piece of unglazed ceramic tile. Like scratch testing, this is destructive and should never be done on a finished gem. If you are using it on rough, the same caution applies. Do the test with a small sample that has been separated from the whole.

This list was meant to be comprehensive. For the beginner all you need is access to our web site, a pair of tweezers and a loupe. These simple tools will take you a long way into the study of gems.


Self Test

1) Gemology involves studying

a) color, hardness and clarity of gems

b) origins of gems

c) physical and optical properties that make gems unique

2) Before setting up a gem lab, reference books should be purchased

a) true- good reference books are essential

b) false- while nice to have, all the information you need is in the IGS Reference Library

3) GIA stands for:

a) Gemology Institute of Atlanta

b) Gemology Institute of America

c) Gemological Institute of America

d) none of the above

4) A loupe is one of the basic tools of gemology. Your loupe should have a magnification of:

a) 5x

b) 10x

c) 15x

5) A triplet loupe is preferred because:

a) it has three aperatures that can be combined for greatest magnification

b) you can view three stones at one time

c) it has three lenses that eliminate distortion near the edges

6) Color corrected in a loupe means:

a) it will match your favorite shirt

b) the loupe contains a special lens to filter out distorted wavelengths of light

c) refers to a special coating on the lens to ensure the color you see is accurate

7) A gem microsope is another essential tool for the gemologist. It has these advantages over the loupe:

a) it is easier on the eyes

b) it will impress your customers (and your credit card company)

c) it’s greater magnification lets you study inclusions in detail

d) all of the above

8) A gem microscope has special features a regular microscope doesn’t have. It should have a minimum magnification of:

a) 30x

b) 40x

c) 60x

9) Besides the RI, the refractometer can also be used to measure:

a) birefringence

b) optic sign

c) none of the above

d) a + b

10) Measuring the specific gravity is also useful in the identification of gems/rough. This can be done by using a balance beam (with one pan in water) or heavy liquids.

a) true – both can be used

b) false- heavy liquids cannot be used

c) is correct , both can be used but heavy liquids will only give an estimate, and are also toxic and flamamable

11) A dichroscope is a small hand held instrument used to:

a) measure the dichros of a material

b) seperate the colors in dichroic material using two small pieces of polarizing material set at 45 degrees

c) seperate the colors in dichroic material using two small pieces of polarizing material set at 90 degrees

12) A polariscope is used with a strainless sphere to determine:

a) if material is doubly refractive

b) a materials optic sign (but not its’ astrological sign)

c) strain and twinning in a material

d) a + c

e) a + b

f) all of the above

13) There are essentially two different kinds of spectroscopes:

a) defraction grating

b) reflectivec) prism

d) a + b

e) a + c

14) A spectroscope with a calibrated scale is preferred but this adds tremendously to the price.

a) true- this makes it much more expensive

b) false- doesn’t significantly affect the price

15) A stone line is:

a) item used to lay stones side by side for grading

b) line of fracture in a stone

16) Jewelers Eye refers to:

a) the look a jeweler gives well heeled customers

b) the ability to distinguish gems from long years of experience

c) an instrument used to measure the luster of gems

17) Hardness points can be used to identify gems and rough:

a) true- can be used effectively for both

b) false- must only be used on rough

18) Streak testing involves the use of:

a) unglazed ceramic tile

b) a brick

c) any hard, coarse material

d) none of the above

19) An ultraviolet light is sometimes useful in making an identification. You will need :

a) short wavelength UV light

b) long wavelength UV light

c) a + b

(Scroll down for the answers)


Answers

1) Gemology involves studying

c) physical and optical properties that make gems unique

2) Before setting up a gem lab, reference books should be purchased

b) false- while nice to have, all the information you need is in the IGS Reference Library

3) GIA stands for:

c) Gemological Institute of America

4) A loupe is one of the basic tools of gemology. Your loupe should have a magnification of:

b) 10x

5) A triplet loupe is preferred because:

c) it has three lenses that eliminate distortion near the edges

6) Color corrected in a loupe means:

c) refers to a special coating on the lens to ensure the color you see is accurate

7) A gem microsope is another essential tool for the gemologist. It has these advantages over the loupe:

d) all of the above

8) A gem microscope has special features a regular microscope doesn’t have. It should have a minimum magnification of:

b) 40x

9) Besides the RI, the refractometer can also be used to measure:

d) a + b

10) Measuring the specific gravity is also useful in the identification of gems/rough. This can be done by using a balance beam (with one pan in water) or heavy liquids.

c) is correct , both can be used but heavy liquids will only give an estimate, and are also toxic and flamamable

11) A dichroscope is a small hand held instrument used to:

c) seperate the colors in dichroic material using two small pieces of polarizing material set at 90 degrees

12) A polariscope is used to determine:

f) all of the above

13) There are essentially two different kinds of spectroscopes:

e) a + c

14) A spectroscope with a calibrated scale is preferred but this adds tremendously to the price.

a) true- this makes it much more expensive

15) A stone line is:

a) item used to lay stones side by side for grading

16) Jewelers Eye refers to:

c) an instrument used to measure the luster of gems

17) Hardness points can be used to identify gems and rough

b) false- must only be used on rough

18) Streak testing involves the use of:

a) unglazed ceramic tile

19) An ultraviolet light is sometimes useful in making an identification. You will need :

c) a + b

See related articles by category: An Introduction to Gemology, Gemology, Reference Library

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