Gemological Microscope

Jewelry Discussion
1

I am making free use of partial articles and wish to thank these
persons, listed and non listed for their contributions. Thank You
very much. - ROBB - Robb Powell .

I made my decisions to purchase my microscopes used at eBay . I did
so after looking for 4 weeks, and shopping on eBay for another 4
weeks I have written about my choices with purchasing a microscope
Here it is.

2 - Quantify - Reichert Stereo Star Zoom Microscopes Model 570 Zoom
range 7x to 42x with WF 10x paired eyepieces Reichert-Jung
articulated boom stand with focusing arm

2 - quantify - Part # 575: .5x Auxiliary objectives magnification
range = 3.5x to 21x with 6" working distance

2 - QUANTIFY - VOPI INTRALUX 4000 HIGH INTENSITY FIBER OPTIC
ILLUMINATORS RING MOUNTED TO AUXILARY SCREW IN 0.5 OBJECTIVE.

I purchased a duplicate microscope so that if I needed work done, I
would not be without a spare microscope And as use as a dedicated
gemological microscope. I purchased both microscopes 2 illuminators,
1 boom stand and sundry other items from MIKE MATHIS wsjcam@aol.com
I was well treated and can recommend this as a place to start
looking.

"AO was bought up by Reichert-Jung and then they were bought by
Cambridge Instruments. At some point, Leica bought up the AO
microscope line along with the Bausch & Lomb line, and then shut down
the AO line. There are lots of used microscope shops around that may
have parts, but it’s a bit hit or miss. Apparently the B&L scopes
were far more common, and are still being made under the Leica name.
"

I am going to include my resources and so everyone
interested can make a choice.

Very good sites well recommended -
ABSOLUTE CLARITY & CALIBRATION, LLC       -    start here !
109 Main Street  v Terryville,  CT  06786
Phone (860) 583-0502 v FAX (860) 314-1851
http://www.absoluteclarity.com/buy&avoid.htm
http://www.absoluteclarity.com/buy&avoid.htm

And here    -     Nikon Microscopes -

Also here - Meiji Microscopes offer a very good value at a
very good price … Meiji Microscopes - http://www.meijitechno.com/

Google Groups
google group: sci . techniques . microscopy
googol group
google group: sci. optics

Southern Microscope Service - http://www.mindspring.com/~smskjc/

The Microscope on a budget -
http://www.mbstevens.com/mscope/index.html#top

Microscope - Depot Microscope-Depot.com Contact Us Page

Light Microscopy Forum - http://www.microimaging.ca/

Nightingale reconditioned microscopes -
http://www.microscopesfromnightingale.com/

" Insider Gemologist: - GIA What are Some Useful Microscope Lighting
Techniques for Identifying Gemstones? "

You can learn more about the identification of gemstones in the GIA
Gem Identification course. For on GIA courses and diploma
programs, click here, e-mail eduinfo@gia.edu
mailto:eduinfo@gia.edu, or call 800-421-7250, ext. 4001.

A microscope offers many more lighting options than a loupe, and
different types of lighting work best for seeing different gem
features. The most useful techniques are fiber-optic darkfield,
brightfield, diffused, surface-reflected, and polarized lighting. An
overhead light source, as provided by a fiber-optic illuminator,
makes it easier to see surface characteristics. Some microscopes
come with a small fluorescent light or allow attachment of one to the
stage for this purpose. You can also use a desk lamp, can be used
with a loupe. For the general observation of surface characteristics,
however, a fiber-optic system like the FiberLite works best. It also
serves as a versatile supplementary light source that is vital for
some separations, especially of synthetics and treatments.

Varying the lighting or using lighting combinations such as
darkfield and fiber optics together can have a dramatic effect on the
visibility and appearance of characteristics, and what can be
determined by examining them. Surface characteristics visible in
reflected light are usually invisible in darkfield light. And
internal characteristics visible in darkfield light are often
invisible in reflected light. Darkfield Illumination

Horizontal lighting created by a GIA Gem Instruments FiberLite
reveals minute flux particles in a synthetic ruby. Most gemological
microscopes have built-in darkfield illumination systems for
examining inclusions. Turn on the microscope=92s internal light source
and close the baffle in the light well so no light can enter the
stone from directly below. Light enters the stone from the sides at
an angle from behind, making some inclusions stand out brightly
against a dark background. The degree to which a characteristic
stands out against the surrounding gemstone is called its relief. For
example, included crystals are minerals trapped within a gem as it
grows. The brassy, metallic surfaces of included pyrite crystals
stand out readily in pale emerald, so they are described as having
high relief. An included crystal=92s relief depends on its refractive
index (RI), its degree of transparency, and often its color,
especially compared to the color of the host gem. A cluster of
moderately sized, colorless calcite inclusions in a blue sapphire
might be much harder to see than a few black chromite crystals
scattered around the interior of a pale green peridot. Most included
crystals are relatively easy to see with darkfield illumination.
Other characteristics, like fluid liquid inclusions-pockets in gems
filled with fluids and sometimes other materials-might require
different lighting techniques because it is often difficult to see
into their interiors using darkfield. Horizontal lighting is a
fiber-optic illumination technique, where a narrow “pinpoint” beam of
light is directed toward the side of the stone. Aim the light
straight at the stone or from an oblique angle. Pinpoint crystals and
gas bubbles stand out as bright objects when viewed from above.

Brightfield Illumination Brightfield illumination-sometimes called
transmitted light-results from opening the light well=92s baffle so th=
e
light is transmitted directly through the stone to your eye. To keep
from being dazzled by the bright light, close the iris diaphragm so
the opening is smaller than the stone. This will create shadowed
transmitted illumination. If necessary, adjust the intensity of the
light source with the rheostat. With the light well baffle open,
brightfield illumination transmits light up through a transparent
stone to your eye (left). Shadowed brightfield illumination is
created by keeping the baffle open and closing the iris diaphragm
until the opening is smaller than the stone. If not properly
controlled, brightfield illumination may make many inclusions look
dark and featureless against an overly bright background. If it is
shadowed by closing the iris diaphragm, however, it works well for
seeing low-relief features like curved striae in flame-fusion
synthetics. Curved striae are structures that represent the layers of
crystal growth around the cylindrical or rod-shaped boule, which is a
typical product of the flame-fusion process.

Shadowed brightfield illumination reveals gas bubbles and curved
striae in a flame-fusion synthetic ruby, while the gas bubbles are
highlighted using pinpoint fiber-optic lighting. The brightfield
technique works best if the light is shadowed by closing the iris
diaphragm and restricting the light source to a small opening
directly under the stone. This allows fine structures like curved
striae to be seen more clearly. Shadowed brightfield illumination can
be created by rocking and tilting the gem under darkfield lighting.
This creates alternating dark and bright backgrounds that can be
helpful for detecting flash-effect colors in fillers-seen principally
in fracture-filled diamond and emerald-or determining if an inclusion
is liquid, solid, or opaque. Rocking and tilting a treated emerald to
alternate dark (left) and bright (right) backgrounds revealed an
orangy yellow to blue flash effect in the filler. Diffused Lighting
Diffused light can be created by opening the baffle and placing a
tissue or a piece of translucent white plastic on the stage over the
well (left). Diffused lighting reveals uneven color zoning and color
zoning at facet junctions in this titanium diffusion-treated
sapphire (right). Photos by Eric Welch.For diffused lighting, open
the baffle and the iris diaphragm and cover the stage opening with a
white, translucent material. Facial tissue or even the white plastic
diffuser from the microscope=92s overhead light source can be used.
Diffused light can help to observe the contents of liquid inclusions
in natural gems. It is especially good for detecting curved color
banding in flame-fusion synthetics. And it is excellent for detecting
uneven color zoning in some lattice-diffusion-treated corundum, where
the facet edges stand out against the white background.

Surface-Reflected Lighting Fiber optics, darkfield, brightfield, and
diffused lighting make many inclusions easier to see, but
surface-reflected light works better for blemishes and certain types
of inclusions. To examine a gem=92s blemishes, position the light
source, which is usually the microscope=92s overhead light unit
(although fiber-optic illumination is actually more suited to this
task and works much better), so the light reflects from the gem=92s
surface. The light should strike the gem=92s surface at close to a 90=B0
angle-this is called vertical overhead illumination. Thin, flat
inclusions-like the thin films seen in many rubies-are also easiest
to see when light reflects from their surfaces. But you cannot use
vertical overhead illumination to see internal characteristics like
these because reflections from the gem=92s surface block the view of
the stone=92s interior. Instead, you need to use a light source-such a=
s
a fiber-optic light-to direct a narrow beam of light at the stone
from an oblique angle. Light entering the stone in this manner
reflects from internal fractures, cleavages, and fingerprints, and
makes them much easier to see without creating distracting surface
reflections.

Polarized Lighting Polarized light can be created with a microscope
by opening the baffle, placing one polarizing filter over the light
well, and holding another between the stone and the objectives.
Rotate the handheld polarizing filter to cross the filters. Polarized
light can be created by opening the microscope=92s baffle and placing
one polarizing filter over the light well and another between the
stone and the objectives. Hold the second filter or attach it to the
microscope just below the objectives. The microscope then functions
as a magnifying polariscope. Use this type of lighting to distinguish
doubly refractive included crystals from singly refractive solid
inclusions or similar-looking gas bubbles or fluid-and/or gas-filled
cavities. Crystals might show interference colors, and are often
surrounded by halos caused by strain, while cavities or gas bubbles
won=92t have these features.

Note From Ganoksin Staff:
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