Colorless Diamond Work-Flow
Known as the ‘Girl’s best friend’, the hardest natural material existing, the most sold among the gems, the most sought-after in jewellery for the engagement rings, the gem with the easiest chemical formula, …to describe diamond are often necessary superlatives. Being the best-selling gem, it is also often the most frequently analyzed in gemological laboratories.
In GIG Laboratory, the journey of a colorless loose diamond starts with an advanced analyses: the Fourier-Transform InfraRed spectroscopy (FTIR), which aims to determine the Diamond Type: Type Ia, Type Ib, Type IaA, Type IaB, Type IIa, Type IIb, ecc.. The Type allows the analysts to understand the Nitrogen content in the diamond and the arrangement of its atoms (if they are isolated, or if they are aggregated and with which type of aggregations), or whether there is Boron. These information are basic because they reveal if there are any chances that the diamond is Laboratory Grown and/or color treated. Concerning D-J colors, until now only a few Types can be created in laboratory. Depending on the FTIR results, if there are possibilities of synthesis or treatments, the diamond will be subjected to further advanced analysis.
If the diamond ‘overpasses’ the FTIR test, the gemologists detect and describe all its characteristics, or rather: they grade it. The grading process is always done by at least 3 gemologists using a ‘double blind-procedure’ based on a lims informatic system. Measurements and proportions (such as table diameter percentage, crown high percentage, crown angle degree, girdle thickness percentage, pavilion depth percentage, pavilion angle degrees) are detected 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.
Inclusions and blemishes are analysed by binocular stereoscopic microscopes and grade at 10X basing on the International recognized Clarity Scale: FL, IF, VVS1, VVS2, VS1, VS2, SI1, SI2, I1, I2, I3. Each characteristic is accurately drawn on a plot reproducing exactly the shape and the cut of the crown and the pavilion of the diamond, following a color code.
The diamond fluorescence is checked with a Wood Lamp equipped with long and short UV lights, 366 nm and 254 nm respectively; even if on the Reports is specified only the intensity of the UVL reaction, in the laboratory docs are reported also the UVS response and the phosphorescence reaction of the diamond after the UV exposure. Fluorescence is always analysed before color, since it can affect the appearance of the color itself.
The color is analysed basically using a set of masterstones; an electronic colorimeter is used to get a further opinion and FTIR data are compared to the analysts’ opinion. It is expressed according to the International Color Scale grade based on alphabetic letters from D to Z.
All the main data are reported on the analyses document issued by GIG Laboratory at the end of the analysis’s procedure; depending on the weight of the diamond, it can be issued an Extend or a Compact version of the Report dedicated to natural diamond.
In case the FTIR analyses points out that the Diamond Type is compatible with treated or laboratory grown diamonds, it is necessary to perform more advanced analyses. To check whether it was created by nature or in the laboratory by man, it’s very useful to use high resolution fluorescence and phosphorescence imaging, which allows to highlight the growth structures of the diamond – very different if impressed by nature or by man. In addition to the imaging, it is also performed a photoluminescence (PL) analysis at Room Temperature (RT) and at Low Temperature (LT) as well. To reach 77K, the temperature required for the LT-PL test, the stone is immersed in liquid nitrogen.
Laboratory grown diamond has a dedicated Report where all the characteristics and the method of synthesis are specified.
The photoluminescence PL analyses is necessary also to verify whether the color of the diamond is enhanced or natural. If these analyses reveal that the color is due to one or more treatments, it will be clearly specified on the Report.
For color treated natural diamond, an extend or a compact version of the Report dedicated to the natural diamonds is issued; for laboratory grown treated color diamond, the Report dedicated to Laboratory Grown Diamond is issued. In both of them are declared all the main data and in the extend versions is also present the plot where is drowned all the inclusions and blemishes of the diamond.