International Gem Society
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TOOLS OF THE GEMOLOGIST
by Donald Clark CSM
Quick Links: Reference Materials - Magnification - Refractometer - Specific Gravity - Dichroscope - Polariscope - Spectroscope - Lighting - Miscellaneous Items
Self Test
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.
| Tools | Importance |
| Gemology Tools | Highly Recommended |
| 10X Loupe | Required |
| Microscope | Required |
| Refractometer | Required |
| SG Scale | Required |
| Dichroscope | Required |
| Polariscope | Required |
| Spectroscope | Required |
| Lighting | Required |
| Gem Cleaning Cloth | Required |
| Tweezers | Required |
| Immersion Dishes | Required |
| Sorting Tray | Required for Grading |
| Calipers | Required for Grading |
| Scale | Required for Grading |
| UV Lamp | Very Useful |
| Chelsea Filter | Very Useful |
| Diamond Tester | Very Useful |
Reference Material
One of the first things you need are 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. This is an encyclopedia to reference gems by name. It does not list them by properties, so you cannot use it as an identification guide.
The encyclopedia is now out of print, but it is worth tracking down a used
copy.
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 significant 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. Also, it is limited to the stones "most likely" to be found in jewelry and it is not comprehensive.
... 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.
Instruments
Magnification
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.
Microscope eye pieces are interchangeable and come in standard sizes. When comparing the power of a microscope, know that you can change magnification by switching eye pieces. This may be less expensive than buying a microscope with higher magnification.
... 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.
Refractometer
A refractometer is an absolute necessity for gem identification. It measures the refractive index of your gems. Besides the RI, a refractometer 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 refractometer as an alternate means to determine the optic sign when necessary.
Refractometers 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 refractometers occasionally come available
on eBay.
Inexpensive models are now available from China for under $200. Their reliability varies, so if you purchase one of these make sure it is from a reliable company that will exchange it. For instructions on how to check the accuracy, see Gem Lab Refractometer.
Specific Gravity
Another gem lab necessity is a means to measure specific gravity, or SG. There are two methods for doing this, both of which are inexpensive. Any scale that is accurate enough to measure to the hundredth of a carat can be adapted to measuring specific gravity. The other method is to use “heavy liquids.” These are a collection of liquids with predetermined SG. 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.
Dichroscope
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 90 degrees to each other, plus magnification.
With a little thought and skill, you can make one yourself. The IGS offers four polarizing filters free with your membership. These are enough to make both a dichroscope and a polariscope.
Polariscope
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.
You can get four polarizing filters for free with a new membership. These are enough to make both a dichroscope and a polariscope.
Spectroscope
If you get serious about your gemology, and specifically gem identification, you are going to need a spectroscope. There are essentially two different kinds, diffraction grating and prism. They both do equally well, but have varying advantages and disadvantages.
Diffraction Grating Spectroscope
With a diffraction grating spectroscope, the light passes through a glass plate with thousands of fine, parallel lines inscribed into it. This disperses the light into its full, visible spectrum. A diffraction grating spectroscope has the advantage that the spectrum is evenly dispersed. However, it is not as bright as a prism spectroscope.
Prism Spectroscopes
With a prism spectroscope, light is dispersed by passing through a series of prisms. It chief advantage is that the spectrum is brighter, which makes faint lines easier to see. It has the disadvantage that the colors are not evenly dispersed. They are bunched up in the red end and more spread out towards the blue. Lines are more difficult to distinguish in the red end, because they are so close together. However, many people feel the greater brightness compensates for this effect.
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.
Some prism spectroscopes come with 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, but you will find that this adds tremendously to the price. This is something you need to weigh into your priorities.
Other factors that adds to the cost are 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 type to learn and the most difficult to use. However, they are highly touted by B. W. Anderson, the father of modern gemology, as "the only spectroscope a gemologist really needs." 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.
Lighting
Lighting 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.
Miscellaneous Items
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 sorting tray, 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 is also a high priority.
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.
Of
course there are other items you can add to your collection. A Chelsea Filter is
common in many gem labs. It was originally called the “Emerald Filter” because
it was used to separate emeralds from look alikes. Now we recognize that its
primary use is to determine if a material gets its color from chromium. There
are other filters that are of some use, but none are a necessity.
If your work
requires you to identify small stones in settings, a diamond tester becomes a
necessity. Small, low quality, dirty diamonds are impossible to distinguish by
eye.
Things You Do Not Need
... 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.
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. You do not need all these instruments to begin your study. 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.
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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) An ultraviolet light is sometimes useful in making an identification. You
will need :
a) short wavelength UV light
b) long wavelength UV light
c) Both long wave and short wave
3) Hardness points can be used to identify cut gems and rough:
a) true - can be used effectively for both
b) false - must only be used on rough
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 apertures 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 microscope 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 can be done by using a scale 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
11) A dichroscope is a small hand held instrument used to:
a) measure the dichros of a material
b) separate the colors in dichroic material using two small pieces of polarizing material set at 45 degrees
c) separate 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, defraction grating and prism
a) True
b) False
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
Answers
1) Gemology involves studying
c) physical and optical properties that make gems unique
2) An ultraviolet light is sometimes useful in making an identification. You
will need :
c) Both long wave and short wave
3) Hardness points can be used to identify cut gems and rough:
b) false - must
only be used on rough
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 microscope 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 can be done by using a scale or heavy liquids:
c) is correct, both can be used but heavy liquids will only
give an estimate
11) A dichroscope is a small hand held instrument used to:
c) separate 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, defraction grating and prism:
a) True
14) A spectroscope with a calibrated scale is preferred but this adds
tremendously to the price:
a) true - this makes it much more expensive
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