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Gemology and Jewelry portal

A selection of gemstone pebbles made by tumbling rough rock with abrasive grit, in a rotating drum. The biggest pebble here is 40 mm long (1.6 inches)

Gemology or gemmology is the science dealing with natural and artificial gems and gemstones.^[1] It is considered a geoscience and a branch of mineralogy. Some jewelers are academically trained gemologists and are qualified to identify and evaluate gems.^[2]

Background[link]

Rudimentary education in gemology for jewelers and gemologists began in the nineteenth century, but the first qualifications were instigated after the National Association of Goldsmiths of Great Britain (NAG) set up a Gemmological Committee for this purpose in 1908. This committee matured into the Gemmological Association of Great Britain (also known as Gem-A), now an educational charity and accredited awarding body with its courses taught worldwide. The first US graduate of Gem-A's Diploma Course, in 1929, was Robert Shipley who later established both the Gemological Institute of America and the American Gem Society. There are now several professional schools and associations of gemologists and certification programs around the world.

The first gemological laboratory serving the jewellery trade was established in London in 1925, prompted by the influx of the newly developed 'cultured pearl' and advances in the synthesis of rubies and sapphires. There are now numerous Gem Labs around the world requiring ever-more-advanced equipment and experience to identify the new challenges - such as treatments to gems, new synthetics and other new materials.

Gemstones are basically categorized based on of their crystal structure, specific gravity, refractive index, and other optical properties, such as pleochroism. The physical property of "hardness" is defined by the non-linear Mohs scale of mineral hardness.

Gemologists study these factors while valuing or appraising cut and polished gemstones. Gemological microscopic study of the internal structure is used to determine whether a gem is synthetic or natural by revealing natural fluid inclusions, and included partially melted exogenous crystals to demonstrate evidence of heat treatment to enhance colour.

The spectroscopic analysis of cut gemstones also allows a gemologist to understand the atomic structure and identify its origin as it is a major factor in valuing a gemstone.

For example, a ruby from Burma will have definite internal and optical activity variance as compared to a Thai ruby.

When the gemstones are in a rough state, the gemologist studies the external structure; the host rock and mineral association; and natural and polished colour. Initially, the stone is identified by its colour, refractive index, optical character, specific gravity, and examination of internal characteristics under magnification.

General identification of gems[link]

Gem identification is basically a process of elimination. Gemstones of similar color undergo non-destructive optical testing until there is only one possible identity. Any single test is indicative, only. For example, the specific gravity of ruby is 4.00, glass is 3.15-4.20, and cubic zirconia is 5.6-5.9. So, one can easily tell the difference between cubic zirconia and the other two; however, there is overlap between ruby and glass.

And, as with all naturally occurring material(s), no two gems are identical. The geological environment they are created in influences the overall process so that although the basics can be identified the presence of chemical "impurities" and substitutions along with structural imperfections vary thus creating "individuals".

Identification by refractive index[link]

Traditional handheld refractometer

One test to determine the gem's identity is to measure the refraction of light in the gem. Every material has a critical angle, at which point light is reflected back internally. This can be measured and thus used to determine the gem's identity. Typically, this is measured using a refractometer although it is possible to measure it using a microscope.

Identification by specific gravity[link]

Specific gravity, also known as relative density, varies depending upon the chemical composition and crystal structure type. Heavy liquids with a known specific gravity are used to test loose gemstones.

Specific gravity is measured by comparing the weight of the gem in air with the weight of the gem suspended in water.

Identification by spectroscopy[link]

This method uses a similar principle to how a prism works to separate white light into its component colors. A gemological spectroscope is employed to analyze the selective absorption of light in the gem material. Essentially, when light passes from one medium to another, it bends. Blue light bends more than red light. Depending on the gem material, it will adjust how much this light bends. Coloring agents or chromophores show bands in the spectroscope and indicate which element is responsible for the gem's color.

Institutes, laboratories, schools and publications[link]

• Institutes and laboratories
  • American Gem Society - AGS
  • Canadian Gemmological Association - CGA
  • Canadian Institute of Gemmology - Cigem
  • European Gemological Laboratory (USA) - EGL USA
  • Gemmological Association of Great Britain - Gem-A
  • Gemological Institute of America - GIA
  • Gemmology Institute of Southern Africa - GISA
  • Gemological Science International
  • International Gemological Institute - IGI
  • Swiss Gemmological Institute - SSEF
  • International School of Gemology - ISG
  • gci gemological centers- GCI
  • Indian Institute of Gemmology - IIG
  • Gemmological Institute of India - GII

• Publications
  • Gems & Gemology

References[link]

External links[link]

• Open School of Gemology

Danielle Perry (born 4 June 1980) is an English radio presenter and DJ currently broadcasting on Birmingham-based Bauer Radio stations Kerrang! Radio and Q Radio.

Perry was born in Bournemouth. She has worked at many radio stations over her ten-year career; she started out reading traffic and travel at Bournemouth-based 2CR FM (now "Heart Dorset & New Forest") and Classic Gold 828 (now Gold) in Bournemouth, before deciding to go to the University of Southampton to study for a BA (Hons) Music degree. After graduating in 2001, Danielle Perry worked with events companies all over Europe, and also started to teach music back in the UK.

In 2003 Perry returned to radio at South City FM (now The Breeze) in Southampton, where she became the stations mid-morning presenter. She progressed through stations on the south coast - including 103.2 Power FM (now 103.2 Capital FM South Coast) and Ocean FM (now Heart South Coast), and also started to cover for holidaying presenters at Xfm South Wales (now Nation Radio), which was at the time owned by Power and Ocean's former parent company GCap Media.

Perry later moved to co-present "The Morning After", the breakfast show on Bauer Radio-owned rock station Kerrang! Radio, with headline presenters Simon James and Hill; the team won silver at the Sony Radio Academy Awards 2009 for Music Personalities of the Year. At the same event, Kerrang! also won gold in the Station of the Year category.

Following the decision by Bauer Radio to move digital alternative music station Q Radio from London to Birmingham, a move which resulted in the departure of several Q presenters, Danielle Perry was selected to host an afternoon drivetime show on Q in addition to her Kerrang! duties. A number of notable musicians have appeared as guests on Perry's Q afternoon show, including Pete Townshend, Tim Burgess, Bat for Lashes, Florence and the Machine, James Dean Bradfield, Kasabian, Maximo Park, The Enemy, The Maccabees, Friendly Fires, Neil Finn and Ian Broudie.

Perry also fronts a series for Q Radio and Q magazine entitled "This Is Who I Am", which is a 12 part interview series broadcast on the radio and transcribed into Q Magazine. Some of the interviewed guests include Ray Davies, Rufus Wainwright, Chrissie Hynde, Carl Barat, Tom Clarke, Kasabian and Beth Ditto. The "This Is Who I Am" strand is a commercially-funded strand sponsored by Orange.

Danielle Perry also has achieved Grade 8 Piano, Grade 7 Flute and studied orchestration as part of her university degree. She has also worked independently as a booking agent and fundraiser for charity gigs around the UK.

References[link]

External links[link]

• Miss Perry Presents
• MySpace - "dscratchperry"
• Kerrang! Radio
• Q Radio
• Drivetime on Q Radio
• "This Is Who I Am"