Gemstone Observation &...
Transcript of Gemstone Observation &...
Gemstone Observation &
Magnification
By Susie Aber
2011-2012
Observation & magnification…
Online Syllabus with links to lectures
http://academic.emporia.edu/abersusa/go340/syllabus.htm
Gem Testing
http://academic.emporia.edu/abersusa/go340/gemtest.htm
Equipment …
Why magnify? What will I see?
• Appraisal – Insurance/ Cut - Polish & Repair :
• Identify, justify, & document gem/jewelry origins to properly
insure or claim
• evaluate/grade as to how fine or rare the piece is… determine
replacement/market value
• fingerprint the gem – plot on diagram facets & inclusions
• Identity by characteristic – origin/growth lines
optical properties-
doubling of back facet
Images from Barbara Smigel,
http://www.bwsmigel.info/Lesson5
/DE.Magnification.html
Why magnify? What will I see?
Justify authenticity – natural/synthetic, enhanced/treated?
Natural rutile silk Pt triangles Stress fractures
colorless sapphire from crucible from high heat
Gems too “clean” or with tiny metallic triangles of a uniform
appearance are usually synthetics… Sapphire is often
heated to get rid of the “silk” rutile… Images from Barbara Smigel, http://www.bwsmigel.info/Lesson5/DE.Magnification.html
Why magnify? What will I see?
Characteristic lily pad inclusions Horsetail like inclusions
Found in peridot – Arizona origin curving asbestos fibers-
mineral bryssolite in
Images from Barbara Smigel, Demantoid garnet -
http://www.bwsmigel.info/Lesson5 Russian origin /DE.Magnification.html
Images from Barbara Smigel, http://www.bwsmigel.info/Lesson5/DE.Magnification.html
Dendritic Chalcedony>
<Vanadinite Drusy
<Rutile Quartz
Images from Barbara Smigel,
http://www.bwsmigel.info/Lesson5
/DE.Magnification.html
Surface & Interior Features can ID
Why magnify… What will I see…
• Expect surprises with magnification! Imperfections are natural… • imperfections in colorless stones affect value negatively
• imperfections in colored stones may enhance value - aligned rutile needles create 6 rayed stars in ruby & sapphire…
• Internal imperfections and inclusions are • Solid, filled cavities/cracks/fissures & crystal growth patterns (color
zoning, banding, or swirls)
• Rainbow effect is internal crystal stress from external pressures- “feathers” can cause the gem to shatter
• External imperfections reflect quality of cut & polish • Symmetry of facets
• Out of round cabochon
• Chips, cracks, scratches
• Conchoidal fracture at drill hole can signify glass bead…
Observation & magnification…
Equipment …
A loupe is a “single lens”
magnifying device, which enlarges
objects to be viewed to ten times its
size (10x – 1 inch focal length). The
triple aplanatic or Hastings triplet is
a high quality lens made of two
external lenses of flint glass (or lead
glass) that is cemented to a double
convex crown glass. Flint glass is
composed of silica, soda, and a lead
oxide and is commonly used in
glass to imitate gems.
The visor fits on head
and allows both
Hands to be free. The
magnification is
Usually 3.5X – 4 inch
focal length.
Observation & magnification…
Binocular stereoscopic
microscope – ocular or eyepiece lenses,
there is an objective lens, which creates
a two lens system to produce a enlarged
sharp image. Magnification is calculated
by multiplying the objective and ocular
magnification (e.g., a 10X objective and
3X ocular produces a magnification of
30 times. Gem microscopes create a
"reinverted" image (regular compound
microscopes invert the image) and
usually have a zoom feature to vary the
magnification. Fluorescent light source
overhead; high intensity light transmitted
up from base.
Maglite shining up
through stone & eye
Looking down through
low magnification
at a comfortable distance!
With microscope – light from bottom:
brightfield for color zoning, dye concentration/
darkfield to highlight internal features
Images from Barbara Smigel,
http://www.bwsmigel.info/Lesson5
/DE.Magnification.html
Same gem –
reflected light from above
darkfield light from below
Images from Barbara Smigel,
http://www.bwsmigel.info/Lesson5
/DE.Magnification.html
Unpolished girdle
with “natural”
Elephant Ivory
Surface reaching fracture
Non-surface
Reaching
Feather in
Tourmaline>
Natural ruby-multiple
fingerprints
Columnar & chicken
wire-prove “man-made”
opal
Stab in heart (above)
Single inclusion (below)
reflected many times.
Fibrous hematite
in strawberry quartz
Diamond in diamond>
< Rough diamond
with internal fracture
Bubbles in moldavite
Bubble in CZ (below)
“Fingerprints” tsavorite
Natural ruby curved
<Straight growth-synthetic flux
Straight color zoning –natural sapphire
Key Steps in Examining a Stone…
• Best to examine unmounted stones
• Be sure gem is free of dirt & dust
• Hold the unmounted transparent stone by girdle
• View under proper lighting • surface features – light source from above
• internal features – light source coming up through
the stone
• Rotate the stone to view at different angles (be
sure you are not looking at the tweezers!)
• Shift stone towards you and away- focusing on
surface and interior
Loupe & observations…
• Hold the loupe to your eye and brings stone close
until in focus
• Have light source from top and side with dark non-reflective
background (dark-field illumination) – with faceted stone
look through pavilion & rarely through table, which can
show the culet but obscures the interior of the stone
• Focus eye on feature and surface – if both in focus the
feature is on the surface; otherwise the feature is below
the surface.
• Observe cut proportions & symmetry of gems and surface
& interior features
This week – online lectures in review…
Gem Lore
http://academic.emporia.edu/abersusa/go340/gemlore.htm
Gem Origins
http://academic.emporia.edu/abersusa/go340/origins.htm
Agate & Chalcedony
http://academic.emporia.edu/abersusa/go340/chalcedo.htm
Gem Briefs
http://academic.emporia.edu/abersusa/go340/gembrief.htm