LAB NOTES - World Gemological Institute
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LAB NOTES

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NEWS & ARTICLES

Ruby Glass -Composites

 

The association between ruby and glass has been documented by leading authority in the field since the Eighties.

Until the 2007 glass was involved only in the heating treatment for rubies with many fractures, cavities and a colour potential; indeed, at high temperatures, it acts as a catalyst and as a filler.During this year, different kinds of samples have been identified as composite of glass and ruby.

In these cases, glass was no longer used only as filler but also as an adhesive. Pieces of rubies were held together by it.

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The pictures show a ruby-glass composite. We can observe a disorderly web of fractures that goes form the surface within the whole stone.

The material in the fractures has a different lustre and texture, and scattered gas bubbles are trapped within.

This filler may be unstable at high temperatures like the bench jeweller torch; that is why special care should be taken when repairing or mounting jewellery with this kind of stones. Imagery and text by Fanny Raponi GG (GIA)

Flux – Grown Synthetic Ruby

 

A synthetic gemstone is a manufactured or man-made material that has a natural counterpart. It has the same chemical composition and crystal structure, and all the physical and optical properties of the natural gem. There are different processes to produce synthetics; in our laboratory, a few days ago we came across this flux- grown synthetic ruby.

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The flux-growth method can be explained easily as a solution of salt and water. Flux is a solid material that acts as a catalyst in the process, it helps to dissolve all the chemical elements needed for the gemstone to grow.

 

As the solution cools, crystals start growing, it is a process that requires around a year and it is very expensive. The key for separating natural from flux-grown synthetic ruby is magnification. The picture shows what we call ‘wispy veils’: whitish fingerprints going into each other disorderly. This flux remnants can be also high-relief, coarse, brownish, yellow to orange, drippy, tubular or icicle-like.  Imagery and text by Fanny Raponi GG (GIA)

Emeralds

 

The Emerald formation is a complex process and it takes place in an exceptionally turbulent environment where rapid changes of growth conditions are common.

It is also peculiar, and remarkably different from the other varieties of the Beryl Species: Aquamarine, Heliodor and Morganite.

 

Emeralds form because of metamorphism (pre-existent rocks are modified by raising temperature and pressure) or hydrothermal process (hot, chemically rich, water solution that forms minerals as it cools in rock veins) or both.

 

This kind of formation causes internal stresses and fractures in the mineral – for that reason fracture filling is a common treatment in the trade. Today there are many different types of filler: oils, resins or compounds, both natural and chemical.

It is crucial to disclose any treatment and the amount of it: minor, moderate or significant; not only because the value changes dramatically but also because the stone could break while it is being set in a jewellery piece or during successive repairs.

 

It is also important to disclose the clarity, since the heat from the jewellers’ torch, chemicals, sudden changes of temperature, can permanently damage the gem, whether if it is filled or not.

 

Even though emeralds have a lot of different type of inclusions that vary on the geology of individual deposits, the geographical origin of a gem is not always possible to determine, as many deposits have the same or similar geology, therefore the inclusions can be similar.

 

The salient examples are the well-known “three-phase” inclusions (liquid, solid and gas together), that until recently were believed to be found only in Colombian emeralds, but a scientific paper from GIA has shown that they can also be found in gems from Zambia, Afghanistan and China.

Thus, the geographical origin is an “expert opinion” based on the observation of intact inclusions and on the results of tests.

 

In the pictures below are shown some natural inclusions, from left and from top to the bottom: two-phase inclusions with a rectangular shape typical of Brazil, hollow tube of amphibole typical of Zimbabwe, Zambia and Russia and mica platelets typical of all the metamorphic emeralds as Zimbabwe and Russia.

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The pictures below show different views of a fracture filled Emerald.

 

From left to right and top to bottom: the diffused light is ideal to gain the whole vision of the stone, the outline of a fracture and an obvious difference in lustre and texture within the fractures, the filler has a shape “branch-like” because it does not occupy evenly all the space in the fracture.  Imagery and text by Fanny Raponi GG (GIA)

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