Invest wisely - Exciting future for coloured stones | EN

The time has gone when on the exchange markets, currency exchange rates fluctuated within narrow margins, on either side of fixed parities. Today, the world is dominated by floating currencies whose sharp unexpected leaps do not fail to disconcert it, in many circumstances. On our old Continent, it is quite certain that the Euro is not stable anymore.

In Europe, prices generally have doubled over the last ten years, indicating that the Euro has lost half its purchasing power. Is there any need to stress on this subject that, in our country, there are investments at a fixed rate of interest, which do not even keep up with the rate of inflation?
And if to this financial unreality are added the gloomy appearance of the world economy, the rumbling of tanks and the sound of gunfire as troops move to the gates of the Middle East, among other places, it is easy to understand the natural reaction of those seeking to make real investments which may in due course show a greater appreciation than that allegedly produced by improved interest.
Let there be no mistake however: gold, diamonds and precious stones do not yield a fixed interest. They have, however, one irrefutable advantage, which is that, in spite of the instability of the international monetary system, the persistence of inflation, that cancer of monetary erosion, they give one the assurance of the realisation of real appreciation, and remain, irrespective of what might happen, a capital of minimal bulkiness, universally and anonymously negotiable.
Why coloured precious stones?
To repeat: let there be no equivocation: an investment in gold, diamonds or precious stones does not generate income. Complimentary investments must therefore be made. Certainly, the appreciation of capital may compensate, and often largely, for the absence of income, but here it is a question of long-term investments and this should not be forgotten.
Having said this, after the spectacular increase in gold prices, the diamond has taken over a major role in the experienced investor's portfolio, and its prices, although without comparison, have in turn experienced large increases. As opposed to the yellow metal, however, the diamond practically never drops in price. However reassuring they may be, gold and diamonds, within the context of this report, have demonstrated that on international markets, they are not protected from speculations, which always represent a real danger in the eyes of investors. On the other hand, it has been found that the coloured stones although perhaps traded more discreetly, nonetheless represent safer and more profitable investments.
Their value is universal, on the same basis as gold and diamonds. The increase in their prices over the last few years ensures the investor of protection from the ravages of inflation.
If gold and diamonds are rare - that is why they are so expensive – precious coloured stones are more so. And whereas the De Beers Company, which monopolizes almost all the Western Diamond market, has decided to launch a new research campaign, representing a prospecting programme of some millions of dollars, it may be estimated that hopes of extracting very beautiful gems will be restricted to thirty years at the very most, in respect of precious coloured stones. Their prices cannot therefore other than increase the nearer that inescapable day comes.
Colour, life, purity
The three main coloured stones, which are most common throughout the world are the emerald, sapphire and the ruby, the last stone is the most rare.
It is at these three types of coloured gem that the investor's choice stops. In the absence of competence or a very long personal experience, it is important to consult a professional in order to make a judicious choice because there is a great variety among the three categories of gems mentioned.
One can nevertheless have some idea by basing oneself upon the four following criteria, which, basically, serve to determine the price of a stone.
Weight, first of all. This is always expressed in carats. The carat is a unit of weight - 0.2 gr., which serves as a standard for jewellers.
After weight, it is colour, which is taken into account. The ruby must be true red, although there are several varieties ranging to pale pink.
It is an error, which is all too frequently repeated, to try and determine the origin of a stone by its colour. A "pigeon's blood" ruby, for example is not necessarily Burmese. It may come from Thailand and may be just as beautiful, if not even more beautiful. A sapphire is not necessarily extracted in Cashmere, simply because it is of a magnificent Imperial blue. It might easily have come from Ceylon, which to day is known as Sri Lanka.
As for the emerald, the most beautiful will be that which has a luminous deep green colour. As opposed to the diamond, it is rare to find pure coloured stones.
By their origin, they contain inclusions, which nevertheless do not constitute essential elements of depreciation for establishing their intrinsic value.
The cut and shape may however contribute to attenuating their effect. It is that cut and shape which adds the flame to the brilliance of the stone. In each quality gem, there is a hidden brilliance whose play and light can be revealed only by the cut and shape.
Whereas, since it belongs to the cubic system, the diamond requires a clever and a cutter in order to show off all its flames, because it is connected to those families of isotropic crystals which only have single refractions, the ruby and the sapphire on the other hand are varieties of the corundum, that is to say of the rhombohedra crystalline system in which double refraction occurs. As for the emerald, this is a variety of green beryl. It belongs to the hexagonal crystalline system. In one or other case, it is the fineness of the cut, which will contribute to showing off a stone, and the experts will, in the first place, observe the way in which this cut has been approached.
It is understood that all these factors play a large part in deciding the prices of coloured stones. In conclusion, it must be stressed once again that trading in top quality coloured stones can only be undertaken with professional jewellers, whose reputation and importance are the bases of a brand image with reflections as pure as those of the most beautiful gems which they may offer you.
Researches have not provided a clear explanation for the colouring of certain minerals. The causes and types of colour in gems remain a very complex problem. Colour is the result of interactions of light-waves and electrons in matter.
The colours of gems are linked with optics, chemistry and recent atomic physics theories concerning the structure and forces of atoms. In mineralogy, the colour of stones is most commonly produced according to 3 types of stone: idiochromatic, allochromatic and pseudochromatic.
- "Idiochromatic" means that the natural colour of the stone is caused by the main element in its chemical composition. Examples: Copper in malachite, iron in almandine. In its pure state, almandine is red, due to bivalent FE2+ iron but should the transaction of metal impurities such as trivalent FE3+ iron occur, the almandine would be black. - "Allochromatic" means other colours. Gems in this category are colourless in their pure state, and the "incidental" presence of trace elements (titanium, chromium, iron, nickel, vanadium, manganese, cobalt and copper) gives rise to an astonishing variety of colour. Most gems are allochromatic.
Initially, rubies have no distinct colour, and the colouring agent is a minimum quantity of "accidental" impurities of chromium. Chrome oxide Cr 203 replaces a very small quantity of alumina. The intensity of red depends on how much chromium is present. Noble red with a dark shade of carmine is the famous "pigeon's blood" colour. It results from the presence of 0.1% of chrome oxide.
The orange hues of certain rubies are explained by the fact that the oxidized state of the chromium is modified by the replacement of trivalent chromium by tetravalent chromium. The other shades of rubies from Siam, such as red-brown or purplish-blue, are due to the presence of iron and vanadium traces. Various factors affect the colouring of minerals: The valence of impurities, the geometry of the crystalline site, the effect of the concentration of impurities, and it will be remembered that chromium is at the origin of the varieties of colour in different minerals. Consider also the allochromatic colouring by the Fe impurity in green quartz.
-"Pseudochromatic" means false colour. The physical causes (and here I should like to refer to the phenomena of diffraction of light in the opal Si02 and H2O, and diffusion in the moon-stone) are at the origin of colour.
Selective absorption of colour:
White light passes through a mineral; part of the spectrum reflected acquires the latter's colour. Light absorbed by the gem, invisible to the eye, could be revealed with the aid of the spectroscope. The same element, chromium, may cause different colours.
Red in the ruby, green in the emerald. The ruby absorbs violet and yellow-green, and transmits red. The emerald absorbs red and violet and transmits green. The electric field surrounding the chromium ions is weaker in the emerald than in the ruby. This causes the absorption band to change position.
It also affects, considerably moreover, the shades of the colour in uniaxial and biaxial anisotropic stones, otherwise referred to as doubly refracting gems (ruby, sapphire, emerald). In isotropic stones (diamond, garnet), the non-absorbed part of light, which produces the colour, does not vary, from whatever angle one looks at the stone.
In a doubly refracting stone, the absorption of light varies according to the direction of the light ray. This variation is known as pleochroism (dichroism in the case of uniaxial gems, and pleochroism in the case of biaxial gems).
The colour of a ruby or a sapphire is determined by looking perpendicularly to the table, and not in any other direction. All this amounts to saying that the colours in idiochromatic and allochromatic stones are due to the phenomenon of transition of elements in accordance with the crystalline field theory, one of the four colour theories.
The other three are the molecular orbitals, the band and the optical physics theories. The classical example in the application of the molecular orbital theory is the deep blue of sapphire due to iron and titanium.
The bivalent iron which is responsible for the blue pigment (the amount varies between 0.01 and 1%) determines the intensity of colour: the tetravalent titanium which produces the subtle shades in the three best colours, kingfisher blue, royal blue, navy blue, occupy the aluminium crystalline structure of the sapphire.
When an electron is transferred from iron to titanium, which means that bivalent iron becomes trivalent and tetravalent titanium also becomes trivalent, this transfer of charge obtains energy of 2 electrons-volt (the unit of energy of the light wave- acquired by an electron when it is accelerated by a difference of potential of 1 volt). These transitions create a wide absorption band from yellow to red, giving the sapphire a very distinct blue.
The band theory applies to chemical substances having an average of four electrons per atom. The bonds are covalent, which means that there is a sharing of electrons, and not the relinquishing of an electron as in the ionic bond. The classic example is the diamond, in which matter contains much less impurity on atomic scale. In fact, the diamond is a semi-conductor with a wide forbidden area (5.4 electrons-volt) which prevents any absorption of visible light, and therefore of any colouring in the pure diamond.
Dispersal (flame of the diamond), diffusion (moon stone), interference (iridescent quartz), diffraction (opal) are optical physics phenomena. Because of the complexity of colours in gems, we conclude that the most effective method of comparing the colour of stones on the basis of a graduated scale would be the use of "master-stones", that is to say, samples.
It is to be remembered that the classification of the diamond in the yellow "cape" series is based on the saturation of yellow with a scale extending from colourless to deep yellow. This normal method, used by the various laboratories throughout the world, is much more conclusive than the calorimeters which are on the market. (Not a valid method for costume diamonds-blue, green, red and the brown series-colourless to maroon).
Be careful not to confuse impurities with inclusions
In the language of gemmology, impurities are defined as being atoms or ions of different natures. They are on the atomic scale and are therefore unobservable. The mineralogist defines impurities by the phenomenon of isomorphism, a phenomenon upon which we shall not dwell. Inclusions are defects, which are visible to the naked eye or under the microscope, affecting the homogeneity of a stone. They may be solid and due to the imprisonment of another mineral during the growth of the crystal (example: "zircon" in the sapphire of Ceylon, pyrite crystals in Columbian emeralds). Columbian emeralds also have two other main types of inclusions: liquid and gas.