Each colored precious stone ( Rubies, Sapphires ans Emeralds ) is just unique.
Like diamonds, coloured precious stones are cut to reflect the maximum amount of light that is cought by the stones. The length of the path on which the light is reflected inside the stone, influences the absoption of light, and therefore the stone’s colour. This means a clear coloured precious stone can have a certain height and a cut in the appropiate shape that elongates the path the light follows inside the stone, which results in a more intense colour.
The opposite is true for a darker coloured gemstone, this must have a more flat shape.
In coloured precious stones, the size is mostly responsible for it’s beauty ; it enhances the colour and personality of the stone. Coloured gemstones have the ablility to reflect the light in different colours, depending on the angle in which the stone is being held. This phenomena is called « pleochronism ». This effect can be weak, medium or strong. This is why the ruby, which has a very strong variation in colour ranging from orange red to deep carmine red, when the stone is observed in different angles.
Inclusions that influence the purity of the diamond and therefore it’s value, don’t have as much of an effect in coloured gemstones. They often even contribute to the visible qualities of a certain stone.
Coloured gemstones are transparent objects, like diamonds. They also absorb, let pass through and reflect the light like diamonds, but in a more modest way.
If a precious stone doesn’t contain any metal, as is the case with pure diamonds, all light passes through. Each metal that is included in the composition of the gemstone (chrome, iron, cobalt, copper, manganese, nickel, vanadium) absorbs a specific wave length in the light directed at the stone. If the stone, like ruby, contains chrome, blue and green in the light are absorbed and the stone appears red. The same phenomenon, but with different chemicals in the composition, appears in sapphires and emeralds.
The extreme variety of metals and amounts of these metals captured in the composition of the stone, is responsible for an infinite choice in colour and hue.
Because of that you can truly say that every gemstone, even more than for a diamond, is unique.
2. Authenticity certificates for colored precious stones
In contradiction to diamonds, coloured gemstones are not evaluated with help of international criteria. Therefore the stones must always be certified by the international laboratories HRD, GIA or IGI after being purchased. The criteria that are most important for this evaluation besides the physical description of the stone (its size and weight) are : origin of the stone, tone, uniformity and vivaciousnes of the colour, purity and size (proportions and symmetry).
Purchasing a coloured gemstone, if the origin of the stone is guaranteed, will always be a very personal and therefore subjective process.