The red gem par excellence, considered a symbol of love, strength and vital energy. One of the most popular and marketed gems and for this reason also more treated, attempting to make it reach the most desired color and transparency. Its journey when it enters the GIG Laboratory is therefore quite long and intricate and aimed at revealing all the changes that it can ever undergo in its history from the extraction to our hands.
All the gemstones submitted to GIG Laboratory to be analysed, including rubies, are photographed. Later on, begin the gemological analyses but, opposite to what happens for diamonds, not by advanced instruments: as for all the colored gemstones, the analyses begin by the routine gemological tools and instruments.
The gemologists start describing the shape, the cutting style, the transparency and the color of the gem. Then they proceed measuring, weighting and calculating the specific gravity. To be as accurate as possible, the measurements are taken using an optical high-resolution measuring system, equipped with a digital camera for the 3D modeling of the stone with interchangeable optical lenses for various stone sizes. The weight is detected basing on a very sensitive and precise electronic scale with 5 decimal places and the specific gravity is calculated using a hydrostatic scale.
Afterwards, the reaction at the polariscope, the refractive index and the pleochroism of the stone are analysed, as well as its fluorescence reaction to both, long and short UV wavelength (366 nm and 254 nm, respectively). Collecting all these data, the analysts have an exact opinion whether the gem is a ruby or not and can then move on to analyze the inclusions using a stereoscopic binocular microscope. Inclusion is everything we find inside a gem embedded during its growth phases and the analyses of the inclusions is essential to understand if the ruby is natural or synthetic (created in laboratory) and whether it is treated or not and which type of treatment/s is/are present/s. By a high-resolution camera set on a microscope, microphotographs of the ruby’s inclusions are also required.
The work done using the routine gemological tools and instruments, is integrated with the analyses carried out by the advanced instruments.
If the microscope analysis leaves doubts that the ruby is synthetic, or even if the analysts are sure it is not a natural gem, as laboratory procedure, it is anyway performed a chemical characterization by an Energy Dispersive X-Ray Fluorescence (ED-XRF) analyses which, basing on the presence or absence of specific chemical elements, will confirm the synthetic or the natural nature of the gem.
It can happen to have treated synthetic rubies artificially fractured and then fracture filled treated. The microscope analyses are fundamental also to detect this treatment, then assisted by an ED-XRF chemical characterization.
Switching to natural rubies, to confirm a typical heat treatment – most of the rubies on the trade are heat treated – it is necessary first of all an in-depth microscope observation and then a Fourier-Transform Infrared spectroscopy (FTIR) analyses is performed to study the vibrational modes correlated with the crystal lattice’s defects or the presence of certain inclusions. Typically, rubies are heated to increase their transparency and/or to change their color decreasing or deleting the blue or brown shade. Sometimes, especially rubies of specific geographic origin such as for example Mong-Shu (Burma), which have many fractures due to their genetic processes, are heated inside a flux substance. This type of treatment enhances more deeply the ruby because it is not only a heat treatment, the flux enters inside the fractures of the ruby healing them and changing the mechanical characteristics of the gem, too. The inclusions accurate observation is also in this case the main important analyses.
Ruby’s fractures are quite rarely impregnated also with oils or waxes. The microscope is always very useful to detect this treatment, but it is possible to use the micro-FTIR system combined with the Micro-Raman Spectroscopy and the fluorescence imaging to help understand the type of material present in the fractures.
Natural and synthetic rubies can both be diffusion-treated, even if it is much more common finding blue sapphires rather than rubies diffusion-treated. This treatment consists in a high temperature heating involving chromium oxide, able to induce a very thin red surface layer in a substantially colorless corundum. It is usually easy to detect it only by the microscope. In contrast, it is much more difficult detecting a bulk diffusion treatment where very light elements as the Beryllium (Be) are involved. These elements are very small and capable of going through the whole lattice of the gem, via diffusion, completely enhancing its color. It is a treatment typically performed on natural rubies to enhance their color. To detect beryllium-diffused gems, the inclusion analyses with the microscope can only offers clues, but not evidences. Due to its atomic weight, the beryllium element is too light to be detected by X-Ray fluorescence technique. The best way to prove a beryllium-diffusion treatment is using highly sensitive chemical analysis instruments such as for example the laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS).
It is also possible to determine the geographic origin of rubies. The work is complex and based on many data. The inclusions analyses carried out by the microscope are always the first performed. Basing on them, the most significative crystals are then analysed with the micro-Raman Spectroscopy which mineralogically characterize them. The chemical analyses are as well important, they reveal information such as for example the Fe/Cr ratio, a diagnostic data that guide the analysts towards some geographic origins rather than others. Other information is carried out also by UV-Vis/NIR Spectroscopy, performed to check the absorptions correlated with trace elements like for example the iron. The collection and a furthered study of all the results acquired, will finally disclose the possible geographic origin of the ruby.
The main data emerged by the analyses are reported on the Colored Gemstone GIG Report, where the client finds clearly stated whether the ruby is natural or synthetic, if it is not treated or treated, in case which type of treatment/s is/are present and, on request, the geographic origin of the gem.