Gem observation

Gemmologists use knowledge, observation to develop expertise. Need to build up a memory bank of visual observation to become experienced. Use various tools from basic to expensive but visual observation is still the most important. Basic - use of 10x lope to assess or identify material. Don't jump to conclusions as might make expensive mistakes or give the wrong information.

Experience in observation is key to understanding gems and aids in ID through the detection of key features.

Observation

Observe with eyes first as some features can be missed under magnification. Record what you see. Many properties are easier to see when its been fashioned according to the beauty factors including cut, shape and polish. Two main types of gem fashioning:

• Faceted - facets are cut and polished flat faces on the surface of a gemstone. Commonly used for transparent gem materials, coloured and colourless. Produces sparkle by reflecting light off the surface and around the inside of the gem
• Non-faceted - includes the general shaping or polishing of objects such as beads, carvings & cabochon.

To observe use a 10x loupe (inexpensive and transportable). When using:

• hold close to your eye and bring the gem towards the loupe until in focus
• Keep loupe and gem steady
• rest the base of your thumb holding the loupe against your cheek and the hand holding the tweezers/gem against that hand
• lean elbow on a table for support, elbows tucked in

Tips:

• hold over a gem cloth in case you drop the gem
• a good lens will provide clear, undistorted view when kept clean with a soft cloth. Aplanatic lens will prevent distortion. Achromatic lens will prevent colour fringes at the edge of field of view. Ideal lens is a triplet lens combining these two features
• if you wear glasses, try without. If can't remember to keep clean
• keep both eyes open and take regular breaks to avoid eye strain

Recording

Good practice to use a white background, good lighting and a worksheet. Steps when looking with eyes:

• 1) describe the colour/hue/tone/saturation. Is colour uniform or is there banding or zoning?
• 2) see if the colour changes when you rotate the stone
• 3) is it transparent, translucent or opaque? what is the lustre?
• 4) observe any dispersion or fire or other optical phenomena eg; iridescence, cats-eye, stars
• 5) document visible external characteristics such as scratches or fractures & internal characteristics such as inclusions
• 6) what is the style of cutting?

Steps for using loupe:

• 1) check colour banding or zoning
• 2) check colour concentrated in fissures that may indicate dye treatment
• 3) document other small external characteristics such as surface reaching fissures
• 4) are there areas with different lustre? these may indicate glass or flux cavity fillings
• 5) is it a composite? any bonding agent or different layers?
• 6) evaluate the polish quality
• 7) document small inclusions and other internal features

Microscopes are used to perform a complete visual observation. Probe further for ID or looking at particular features. Modern microscope is a stereo binocular microscope. Uses both eyes to decrease eye strain and gives an object a more 3D appearance. Rarely need to go above 100X magnification. With a gemm'l microscope you can vary focus / vary magnification / vary light diffusion from top or sides / vary aperture (amt of light getting through).

Handling

When using tweezers/tongs experiment to see what suits you. Use grooved tips for holding securely and fine points for smaller stones. Larger pieces can be held by hand.

Stones can spring off so it is good practice to take a gem and lay it face down (table down - table is the top, flat facet) on a flat surface, the pavilion points up (the pointed end the the cut gem). Pinch the sides of the gem gently with tweezers. Be mindful of the pressure you exert on the gem. Just enough to hold securely. With grip or sliding lock tweezers be careful not to push the grip too far as it may damage the stone.

You want light bright enough to see what you need but not too bright to get glare. can use desk lamp or a small, bright torch (often carried by gem'ts). Never look directly at a strong light source through the loupe. Practice to hold the gem in the right position relative to the light source, your eye and the loupe.

Can use light to shine through the stone to view its colour or internal features. Other times use light to reflect off to see the surface.

Important to examine the surface of a gem. Loupe may reveal variety of external features such as cracks, wear, polishing lines, impact chips. These surface features can help ID a stone and warn of issues affecting durability. Eg: paste shows worn features, rounded edges, scratches and sometimes mold marks (where glass has been cast to shape rather than cut. Molten glass is poured into a mold). Harder gems will be less scratched but can still show wear if they are old or mistreated.

Care

Gems can be broken, damaged by household chemicals or sudden temperature changes eg: emerald, opal, peridot and tanzanite don't like thermal shock which can cause them to break and shatter - don't leave in the sunshine and avoid heat. Some gems will fade with lengthy exposure to the sun. Some gemstones need more careful handling, like amber which is soft and won't tolerate solvents or heat (can melt at low temperatures).

Often ,may not be the gem that suffers directly but the material used to improve it, such as fillers, oils or coatings used to stabilise a gem. Weak acids can leave pitted surfaces and a loss of sparkle. Avoid solvents, like acetone or alcohol, as some dyed of filled stones can be affected. Some treated stones may be more susceptible to damage, as the treatment itself can affect toughness, stability or durability.

When wearing jewellery remove if you are doing any laborious task or playing sport, particularly if the gem has perfect cleavage. Due to cleavage properties, for example, some gems are recommended for certain settings and not others, eg: earrings and not rings or bracelets as they are less likely to be knocked about.

Treat all stones as fragile and handle carefully to last longer. To clean:

• luke-warm water
• mild liquid soap
• over a bowl - not the sink
• soft toothbrush to carefully loosen dirt
• be careful around mounts
• dry with a soft & lint-free cloth or air dry

Be careful with electronic cleaners (eg: ultrasonic) and general use of chemical cleaners or solvents. Ultrasonic baths are filled with water and cleaning fluid into which you put the item to clean. High frequency soundwaves pass through the liquid & vibrations remove the dirt. [Use ear protection to protect yourself from the vibrations]. Some gems have minute inclusions which can be damaged and then crack therefore decreasing clarity. Electronic cleaners can:

• cause chemical damage
• cause cracks to appear
• damage stones treated with oil/dyed/filled
• loosen or detach stones from mounts

Best stored in individual boxes to avoid abraiding against each other. Very expensive gems can be stores in a safe deposit box. Gems are a valuable asset regards finance, legacy and emotion, so regularly clean and repair if necessary.

Light

[see also Gem Properties for section on Light]

White light (eg: sunlight) is made up of wavelengths of energy corresponding to different colours. These can be seen when white light passes though/reflected by certain objects such as raindrops. In gemstones light can be reflected, pass through or absorbed. White material reflects or transmits, all white light; black material absorbs light (so looks dark); coloured material absorbs some wave lengths and remaining unabsorbed are transmitted to our eyes giving colour = 'selective absorption'.

Colour is a combination of hue, tone & saturation. Hue - the basic colour we see (eg: red, green) / tone - how dark or light the hue is / saturation - intensity, how bright or dull it looks.

Nature of light has been debated. 1) behaves like a wave or 2) like small particles of energy (like bullets being fired from a gun), these particles being called photons. Both theories are now used in explaining light behaviour. Scientists define light as a type of radiation (electromagnetic) known to travel in a vacuum at c. 300,000km/second. Visible light is a small portion of electromagnetic spectrum, which includes radio waves (low end of the scale) to gamma rays (highest end). Visible light has various levels - dark red (lowest we see) then orange, yellow, green, blue, violet (highest we see) then ultraviolet or UV. Can see the effects of UV - object absorbs UV and emits the energy at a lower level resulting in a 'glow' that we see.

Understanding light is critical to understanding gem techniques. As well as visible light, some techniques use other portions of the spectrum (eg: infrared) to help discover the true nature of gem materials.

Initially people didn't differentiate between gems of similar colours then realised that different stones can have similar colours eg: natural aquamarine is similar to syn. blue spinel - very different materials with different natures.

Need to properly illuminate a diamond to bring out its visual characteristics. Critical to illuminate a star or cat's eye with a single, strong light source. Properly illuminating loose gemstones and set stones is important in a salesroom setting. Ensure light does not over exaggerate colour as the gems will look different after leaving the room.

Diamond and colourless gems

If white light passes freely through it looks colourless, eg: diamond. described as brightness/brilliance, which is the visual appearance of the internal and external reflections of white light. The round, brilliant cut remains popular as it gives the maximum light return.

Important to move the gemstone to see how it reacts to light. In diamonds we see 'scintillation' = sparkling effect created by alternative reflection of light and dark on the facets. There is also 'fire' or flashes of colour. A diamond with high fire is a substance with large reflective power and can end a ray of white light into spectral colours / colours of the rainbow (= dispersion). These are visible depending on light path and angles through the gemstone. Also seen in zircon and demantoid garnet.

Can refer to a colourless diamond as a 'white diamond' but most are not true white - only the rarest are. The more white / colourless are the preferred.

Visual appearance of a diamond depends on quality of its cut, shape, proportions, symmetry, polishing quality & the light environment when being observed. Strong direct light it appears dark & grey but can bring out scintillation & fire. Diffused light reveals brightness & apparent whiteness (not fire or scin.). Want a compromise of these two when displaying a diamond to bring out its best. Colourless diamond will mirror the environment around it, which is why planning illumination of a display is important. Plan the lights to show - whiteness, brightness, scin. or fire, and use combination of white background & direct or diffused light. With sales it can be useful to view stone outside to see how they look in different light.

Optical effects

Light interaction causes a variety of optical effects in gemstones. 'Phenomenal stones' is the term used and includes cat's eye, star, play-of-colour. Effects can be used as diagnostic features in identification.

Single strong light (good point light) is used to bring our the best in these stones and why gem dealers choose single light source to display them.

Cat's eye:

• 'chatoyancy' (French) consists of single line or bright band of light hovering above a curved polished surface.
• caused by reflection of light from one orientated set of parallel internal structures, such as needle-like inclusions.
• best know gemstone is chrysoberyl (in the trade 'cymophane')

Star:

• known as 'asterism' (Greek and Latin for star is aster).
• reflection effect seen as two or more bright bands / sets of parallel structures cross at angles to produce a star.
• seen on cabochon cut gemstones & polished spheres.
• may see four-rayed stars (eg: black diopside), six-rayed (ruby or sapp), twelve-rayed (rose quartz).
• must plan the appropriate cut to obtain a more desirable, centred optical effect.

Play-of-colour:

• notably seen in precious opal.
• a type of iridescence caused by interaction of white light with the material structure, causing wave length interference. The result of light travelling through or being reflected & diffracted (bent) by surfaces of thin layers or cracks.
• some colours in the reflected light are cancelled out while others are boosted.
• iridescence (Greek for rainbow) is seen on soap bubbles and oil films.
• precious opals internal structure consists of rows of minute spheres which are the perfect size to interact with light waves and cause interferences, especially when the stone is moved and tilted.
• Moonstone - light reacts with thin layer of material to give a play of light. Pale, blue glow come from just beneath the surface as gem is rotated. Light interacts with tiny different changes in the mineral layers to give a shimmering effect called adularescence or schiller.

Opaque

Generally opaque gemstone are not cut from single crystals but from stones composed of numerous minute crystals / layers of think crystals eg: lapis lazuli or agate. Light is broken up / deflected by this type of structure and doesn't pass freely through.

Jade can be cut as cabochons or cared. Prized in Asian cultures for its magnificent colour eg: translucent, deep emerald green to softer hues of lavender and white.

Opaque and translucent gems are not just cut as cabochons but also beads, small carvings & inlay in ornaments and furnishings.

Colour

Perceived colours results from absorption of certain portions of visible light spectrum and dependent on light conditions (artificial, different geographical location, time of day). Various mechanisms cause colour in gem material but usually related to chemical composition, including presence of minute amounts of elements that cause colour, the gem's internal structure or abundant inclusions.

Paraiba tourmaline - most desirable electric-blue caused by large amounts of trace elements like manganese and copper.

Understanding colour causing mechanisms requires use of spectrophotometer and interpretation of data it collects. Can use a handheld spectroscope, where you see which portion of light is being absorbed, to aid ID.

Multiple colours

Pleochroism = many colours in Greek. Is rarely diagnostic but can help decide what further tests to do.

Most gems are crystal therefore built of regular atomic particles. These patterns affect how light passes through - in some directions light passes easily, not so in others. Depending on the gemstone species the overall colour is a combination of colours resulting from how the stone absorbs lights along different directions eg: Iolite, which looks blue in one direction and almost colourless in another.

Dichroscope:

• enables you to see the colour changes of a transparent, coloured gemstone. Helps in ID eg: red spinel will show only 1 colour while a ruby will show two (orange-red and purpley-red).
• two types. Easiest to use is the 'London dichroscope', filter made of similar material as polaroid sunglasses. Filter is divided into two & if there is pleochroism it will show as different colours or shades, through the two sides.
• gem showing two colours = dichroic
• best result when have stone on a light table or portable flat lamp.
• 5 tips for use 1) hold it near the stone not the eye 2) move a little from side to side 3) view the stone from different directions 4)don't use direct sunlight as its slightly dichroic 5) use bright, diffused light behind and make sure it passes through the stone the stone.

When a stone is cut may want the best colour to come out of the top of the stone so you can see it with a pleochroic stone, one viewing direction may be more desirable. If a gem is not cut of crystalline material then you don't see directional light properties (glass gem imitations don't show two colours with a dichroscope). If a gem is from a crystal with uniform pattern of atoms in all directions than also don't see two different colours (eg: spinal or diamond). If gem is from crystal with a pattern of atoms that varies in different direction then will see pleochroism (eg: ruby or emerald).

Some gems can appear to change colour when illuminated by different lighting (eg: shop lighting or daylight) = colour change gems. When observed colours are adjacent hues, there is a colour-shift on the colour wheel. When the colours are far apart on the colour wheel = true colour change. Stones showing food contrasting colours are highly prized and expensive (alexandrite effect). Alexandrite is most famous for this (others that may show it are sapphire/garnet/spinal):

• a variety of mineral named after Tsar Alex. II, mid 19th century.
• appears green in daylight and red in candlelight - emerald by day and ruby by night.

Tools (loupe and dichroscope) are used for observation and can help eliminate what a gem may or may not be. Reason to carry an incandescent light source is to spot colour changes.

Fluorescence:

• 'luminescence' is the emission of cold, non-incandescent, visible light. One type is fluorescence - may be seen in some gems and those treated.
• rubies will glow vivd red and some diamonds look bright blue.
• seen with UV light. During gem testing you record a gem material's reaction the UV light

Magnification

Transparency and clarity are important to value. The majority of diamonds are graded for lack of colour and clarity. 'Eye clean' means no flaws visible to the unaided eye. Inclusions common in emeralds and rubies but not common in aquamarine or zircon. There are small inclusions in many gemstones

With a loupe, correct lighting and practice you begin to understand the relevance of what you see. In a transp. gem up to 90% of gem ID can be done with a loupe, if experienced. But in other cases inclusions are too small so you need magnification. Gemm'l microscope provides:

• higher magnif. than a loupe.
• ways to adjust & optimise the light to pass through the stone so to view it at its best.

Inclusions

Examples:

• rutile needles (fibre-like). Found in unheated or low heated sapphire. Can reflect the light to give optical effects.
• three phase inclusion is solid (eg: square crystal), gas (round bubbles) & liquid. can be indicative of emerald from a specific location.
• tapering mica within Morganite ; mica in emerald
• circular tension halos caused by stress and damage around an inclu. from radiation or by slight heating.
• horsetail - radiating fibrous inclu. Indicative of demantoids from Russia.
• straight colour zoning indicative of natural sapp.
• tiger stripe in quartz-amethyst
• heat treatment induced internal fracture, with glassy discoid appearance in a sapp.
• flux-assisted healed fracture in a ruby. Undergone heat treatment process where glassy residue marks where the fracture used to be.

Factors to consider for clarity and inclusions:

• observe with eyes, from different angles.
• then use magnif. with good light source. Prefer diffused as filament light gives reflections. Angle light from side and slightly from bottom = darkfield illumination. Helpful when using a micros., to highlight inclu. under a loupe & to view overall transparency.
• reflect light off the stone to view the surface to see cracks, blemishes & any joins between material that have been glued together or polished. Dark stones can hide flaws. Lighter stones should have better clarity.
• compare like with like. Eg. emerald with emerald not emerald with tsavorite which have better clarity. This way you see the range of inclusions a family of stones has.
• be vigilant with set stones. Along with careful cutting, the mounting may hide inclusions or cracks.
• most times when using magnif. there are observable inclusions but material of very high clarity will require checking with other techniques.

Formation of inclusions - Protogenic - before a gem is formed / Syngenetic - at the same time / Epigenetic - after it formed.

Varieties include solid crystals, clouds, needles, cracks, cavities, silk, halos, fingerprints, fluids, growth zoning, chips - and combination.

'Diagnostic inclus.' are present & distinctive in a few specific gem materials. eg: horsetails in green demantoid garnet / thread-like fluid inclus. called trichites in tourmaline / disc-like lily pads in peridot. Example case study: transparent, purple stone could be amethyst quartz, syn. amethyst, glass or scapolite. Use a loupe & inspect the interior and surface. See no bubbles which would indicate glass but do see ribbon-like rows in tiger or zebra patterning ('tiger stripes'). These are partially healed fissures that developed along certain directions, and are known to typically occur in natural amethyst.

Inclus. can be an important characteristic to determine nature of a gem (natural, syn., treated) or where it came from. Can provide evidence of how a gem grew. Synthetic gems differ in the amount of time they have taken to grow. Naturals can take millions of years to grow. Synthetic, lab grown, the process is sped up to become economically viable. This fast growth leaves some evidence under magnification.

One example is curved zoning in syn. rubies:

• oldest commercially viable ruby is called Verneuil 'flame-fusion syn. ruby'.
• created c.1900 and still in production today for inexpensive jewellery and wrist watch mechanical movements.
• a powder of aluminium oxide with small amounts of chromium (for colour) is superheated in a furnace and droplets fall onto a rotating stage below.
• stage is lowered gradually and molten drops fall on top to form a cone of corundum which cools and crystallises quickly.
• this is called a 'boule' from which gems are cut.
• the growth method results in development of sub-parallel curved zones seen if looked for. Natural rubies ave straight growth zones.

Origin determination:

• historically popular gemstones often came from particular regions and these are recognised as prestigious & desirable.
• there is a relationship between a stone's gemm'l properties (like growth features), inclusions & place of origin. With this recognition, the market saw an opportunity to promote a gem's provenance beyond known history of possession.
• work has been done to build a database of characteristics to help determine origins. Early on this work benefitted from the fact there were few commercially significant deposits or regions that produced the gemstones. There were instances where certain features were thought to occur in stones from only one/minimal localities.
• more recently new gem occurrences have revealed inclusions thought unique to one location, are found in a number of other places. Therefore inclusions are no longer used to make determination about geographical origin.