International Gem Society
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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.
... 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) reflective
c) prism
d) a + b
e) a + c
14) A spectrascope 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)
Return to
the Top of the Page - Return to the Reference
Library
...
...
...
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 spectrascope 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