LAB NOTES - World Gemological Institute
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LAB NOTES

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About Enhanced Color Diamonds

 

Yes, They Are Real Diamonds.

The first thing you need to know about enhanced color diamonds is that they are real, not synthetic diamonds. Typically, enhanced color diamonds start out as nearly colorless diamonds in their raw state. They then undergo a color-enhancement process using irradiation or HPHT (high temperature, high pressure).

Enhanced diamonds are more affordable than white diamonds. This is not because the diamonds used to produce enhanced colored diamonds are flawed. It is simply that the best candidates for enhanced color diamonds are those that already have some coloring and are not entirely white.

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The history of enhanced colored diamonds

In the 19th century, the world supply of natural color diamonds simply couldn’t meet their demand. Their scarcity meant extremely high prices, and were therefore accessible to only those with great wealth. Soon, scientists experimented with methods that would add color to white diamonds in order to make colored diamonds more available and at a more affordable cost to the public at large. Although color enhancement was first successfully developed in 1904, it wasn’t until the 1950s that enhanced diamonds became popular. This came about as the enhancement process became simple and safe enough to be done in commercial quantities. More recently, the development of the HPHT process has also meant that an even further range of colors can be reached.

Use, Care and Cleaning of Irradiated Diamonds

Irradiated color diamonds, like all diamonds, are unlikely to change unless they are subject to temperatures above 450 C/ 850 F. Generally, a diamond will only be exposed to these high temperatures at the jewelers bench when resizing a ring.

But there are some points to be aware of regarding the setting and care of irradiated colored diamonds:

 

Settings

Irradiated colored diamonds can be set in almost every possible style of setting including, channel, prong, invisible, bezel, flush, or pave. However, irradiated colored enhanced diamonds cannot be wax-set because that process involves high temperatures.

 

Cleaning

The surface of an irradiated diamond, like all diamonds, can come in contact with in everyday dirt and grime such as hand lotions. If this does happen, Irradiated colored diamonds can be cleaned just like regular white diamonds. They can be cleaned using steam, ultrasonic, acid or any jewelry cleaner. To clean a colored diamond at home, use a soft toothbrush and soapy water.

 

Exposure to High Temperatures Over 450°C (900°F)

When a ring with an enhanced color diamond is being resized, it is important that it be treated with the same care as a precious color gemstone, such as an emerald. The stone must be protected from direct exposure to high temperature over 450°C (900°F). Such high temperatures can adversely affect the color of an enhanced diamond. An experienced jeweler will cover the stone with either a saturated mixture of boric acid and denatured alcohol or a special protective paste such as a product called, Heat Shield. Either option will adequately protect the diamond during bench work from direct exposure to the high temperature generated by a jeweler’s torch.

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 (G.G GIA) WGI Head Gemologist. (2017-2019)

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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 (G.G GIA) WGI Head Gemologist (2017-2019)

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 (G.G GIA) WGI Head Gemologist. (2017-2019)

Understanding Fluorescence

 

Let’s start defining what is this phenomenon:

Fluorescence is the visible light some diamonds emit when they are exposed to UV rays, and on WGI reports it refers to the intensity of the diamond’s reaction to Long-Wave UV which is an essential part of daylight.

The 25 – 35 % of diamonds exhibit fluorescence* and in 95 % of the specimen the colour seen is blue but can be any colour.

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Aurora Pyramid of Hope, Natural History Museum in London, shows 296 naturally coloured diamonds and how they change under Long Wave UV light.

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Picture of an antique and a modern piece of jewellery as seen under the Long Wave UV light, they show a great variety of colour and intensity of fluorescence.

 

In the trade Fluorescence is perceived as a negative property although, when a medium to strong intensity is present the diamond looks whiter and brighter in daylight. This means it can appear one or two colours whiter.

 

Only in extremely rare case when the fluorescence is very strong, diamonds could appear hazy or milky.

Hence Fluorescence is just a characteristic of diamonds, like the chemical composition or crystal structure, and not a given grade, plus it does not affect durability, clarity or value. Imagery and text by Fanny Raponi (G.G GIA) WGI Head Gemologist. (2017-2019)

 

*https://4cs.gia.edu/en-us/blog/understanding-diamond-fluorescence/

Fracture Filling in diamonds

 

Fracture filling is a common treatment for diamonds to enhance the clarity but, being not permanent it only improves the appearance.

 

What is it exactly?

It is a molten glass filler that has a Refractive Index (RI) very close to the diamond’s RI, it means that the feathers/fractures are less visible.

As with every other treatment it is important to disclose: it affects the value; deep fractures, even if disguised, can affect the durability and, if the diamond is mounted in a jewellery piece, the temperature of the jeweller’s torch or sudden changes of temperature can damage the filler or cause the filler in the fractures to expand.

 

Which are the visual indications? And how is possible to detect them?

In gemmology what we call “flash-effect colours” are flashes of blue/violet or yellow/orange that occur within the fractures.

Sometimes the amount of fractures is so high that is possible to see these flashes with naked eyes through the table of the diamond, but usually, it requires a thorough inspection with the microscope or at least with the 10X Loupe.

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The best way to see fracture filling is through the pavilion, holding the diamond table to culet.

 

Why is it necessary to submit your diamond to an independent Laboratory?

Because the “flash-effect” can be mistaken for the natural iridescent colour seen in fractures, when the air interacts with the light.

Below from left to right a fracture filled diamond and an untreated one. Imagery and text by Fanny Raponi (G.G GIA) WGI Head Gemologist. (2017-2019)

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Rough Diamond Simulants

Some days are more exciting than others and this was one of them, feeling like detectives in our lab.

We received two rough stones, octahedral shape, labelled as “rough diamonds”.

Something caught our attention: on the octahedral sides, there were big triangular marks that pointed at the same direction as the facets.

We can see from the pictures below these marks are obviously carved, the lustre is much lower than the one of a diamond and the edges of the marks are not sharp proving a lower hardness.

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The pictures below show genuine trigons: crystal structure’s growth marks

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In the second rough there were visible many features that proved its different species.

In the pictures below we can see many two-phase inclusions (gas and liquid together) typical of the hydrothermal formation that implicate a much lower temperature and pressure than the ones needed in diamond’s growth.

 

These inclusions are a hunch that the specimen can be a Beryl, a Quartz or a Topaz.

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Through other testes we eventually identified the two roughs as the first Colourless Sapphire and the second Colourless Topaz.

 

In this picture the Colourless Sapphire seen under the polariscope with conoscope shows a typical uniaxial optic figure that remind a cross (concentric circles called isochromes and two L shapes isogyres). Imagery and text by Fanny Raponi (G.G GIA) WGI Head Gemologist. (2017-2019)

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