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Imitations, Substitutes and Treatments Of Stones And Gems: The Trap to Avoid

As the market for gems, jewelry has become more globalized, treatments are evolving ever faster and are increasingly difficult to identify.

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Every day, we are solicited by a rigorous and demanding clientele who are confronted with substitutes or imitation stones. Not to mention that the market, in a few decades, will be flooded by laboratory diamonds.

My degree in gemology allows me to work with imitation stones every day. Here is a summary of the different types of stones that can be substitutes to natural stones:

 

Imitations:

Imitations have a similar appearance to the imitated stone. They have little or no physical, chemical or optical characteristics in common.
Since antiquity, there have been many substitutes for gems such as glass, which the Egyptians were the first to produce.

Today, rhinestones, i.e. leaded glass, are still used to imitate diamonds, as the lead makes the glass shine. Many other imitations of diamond are widespread on the market.

I would mention some artificial crystals that have physical and optical characteristics in common with diamond: synthetic strontium titanate, YAG (Yttrium Aluminum Garnet), GGG (Gadolinate Gallium Garnet), linobat and synthetic zirconium oxide which is particularly flooding the market. We must not forget a more recent imitation which is the synthetic moissanite marketed since 1997. This stone has a hardness, a luster, a thermal conductivity close to diamond.

The thermo conductivity meter and the reflectometer are unable to differentiate between a diamond and a moissanite.

synthetic-moissanite
Synthetic moissanite

 

Doublets:

Doublets are stones called “assembled”.

There is the DGV (Doublet Garnet-Glass) which is a stone consisting of a piece of glass and a strip of garnet Almandine.

We can also cite the Doublet Enamel consisting of two pieces of rock crystal, synthetic spinel or beryl and between the two at the level of the laminate a strip of enamel.

enamel-dgv-doublet-diagram
Enamel and DGV doublet diagram

 

The Doublet Fine Corundum-Synthetic Corundum also exists, it consists as its name suggests of two stones: one natural and one synthetic.

 

Synthetic stones:

Synthetic stones are produced in laboratories with almost the same physical, chemical and optical properties as natural stones.

For emeralds there are mainly synthetic anhydrous emeralds and synthetic hydrothermal emeralds.

To identify the hydrothermal emerald, only the binocular can make the diagnosis.

The family of corundum including rubies, sapphires, colored sapphires is also the target of many syntheses: synthetic Verneuil corundum, synthetic anhydrous corundum, synthetic hydrothermal corundum, synthetic Czochralski corundum (method by pulling) and many others.

The Verneuil synthetic corundum is particularly used and mounted on many jewelry and even very old jewelry since they were industrialized in 1902.

Its principle is as follows: An alumina powder mixed with a coloring agent is heated to 2000°C in a furnace.

The drop formed at the end of the flashlight falls on a small base on which a crystallization seed is placed where it crystallizes and gradually forms a bottle.
Very large stones can be cut from these Verneuil synthetic roughs. This synthesis can even be used to make sapphires or star rubies!

verneuil-synthetic-ruby
Verneuil synthetic ruby

 

The Verneuil synthesis is also used to make synthetic spinel.

Synthetic rutile, also called titania, is used as a substitute for diamond and has been marketed since 1948. However its dispersion is 6 times higher than the diamond.

 

The industrial synthesis of diamond was successfully achived in 1953-1954 in the United States and Sweden.

In recent years, between newspaper headlines and radio broadcasts, everyone has heard about synthetic diamonds, also known as laboratory diamonds or “lab grown”. Unfortunately, only gemological laboratories such as the LFG, GIA or HRD are able to authenticate a synthetic diamond.

This remains a huge problem for our profession because the profusion of synthetic diamonds used in jewelry making process will soon be impossible to detect with only our tools and magnifying glasses.

Today, practically all gems have a matching synthetic diamond that can be marketed.
The profession authorizes the commercialisation of synthetic gems, there is even a market and a demand. On the other hand, the certificate issued by the trader must mention that the stone is a synthetic one, as well as the treatments which must be specified on the invoice.

 

Reconstituted gems:

Reconstituted gems are materials obtained from small pieces or powder of natural gems by different processes: by pressure, fusion, sintering, cementing etc…

Turquoise is unfortunately the target of this technique which somehow is a fallacious way to commercialise it.

 

reconstituted-turquoise-beads
Reconstituted turquoise beads

 

To improve already existing stones, Man has created treatments, from the lightest like heating to the heaviest like irradiation.

 

Thermal treatments:

Heating is mainly used for corundum.

It improves the color without adding foreign bodies inside.

The technique called Bata Kubala or Blow Pipe has been used in Sri Lanka for many centuries. Being a light treatment as the temperature is still far from the melting temperature of corundum, it is not required to be reported on a certificate.

Heating can be spoted by a qualified gemmololist due to the physical presence of dried butterfly wings inclusion inside the corundum.

Since the 1960’s, heat treatments at much higher temperatures have appeared. Acting on the physico-chemical structure of the stones, they are much more problematic.

 

The filling:

It consists of filling the stones with lead glass to improve their transparency. Thanks to this treatment the gems we obtain has a color worthy of the most beautiful stones, even though the gem was originally unusable in jewelry. Unfortunately these stones have flooded the market. It is however fast to identify them.

 

ruby-treated-with-lead-glass
Ruby treated with lead glass

 

As a type of filling we also have the oiling of emeralds, a treatment that concerns the majority of emeralds.

This treatment is not a problem because emeralds are very fragile. But if the oil is replaced by resin, the treatment is no longer considered in the same way, the resin is irreversible unlike the oil and it can also be colored.

It is possible to obtain beautiful mint green emeralds from emeralds that are much less beautiful in nature.

 

Diffusions:

There are the simple diffusion and the deep diffusion.

The principle of diffusion is to incorporate at very high temperature chromophoric elements in the stone to make it more colorful. The simple diffusion is more on the surface than the deep diffusion.

diffused-sapphire
Diffused sapphire

 

Irradiation:

Today many stones are irradiated with high electromagnetic energies such as X-rays, Gama…

These are very heavy treatments used to make colored diamonds, topaz London blue etc. …

irradiated-topaz
Irradiated topaz

 

Many other treatments exist and are becoming increasingly difficult to detect. The world will never stop developing more.

 

Nowadays the best way to guarantee the authenticity and the quality of a stone is to refer to graduated gemmologist.

Gemmological laboratories are also authorized and requested to establish a certificate.

In Paris the most recognized laboratories with which I work daily are:

Abroad:

 

You want to know the value or the quality of a precious stone?

Pierres de Julie will carry out a first estimate or a free oral expertise. If you wish to obtain a written certificate of authenticity, you will need to make an appointement.

We will be happy to welcome you in our boutique in the Swiss Village in the 15th arrondissement of Paris.

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