By: Іgor Iemelianov, Katerina KORMAKOVA. State Gemological Center of Ukraine
The authors have highlighted some issues related to natural and synthetic diamonds in previous publications. Brief historical information on the first attempts to obtain diamonds in laboratories have been given as well as the overview of the main methods of synthesis, the crystal morphology of natural and synthetic diamonds were considered, the principle of operation of the Diamond View TM device was described. In this article, we will continue to open up the opportunities of Diamond View TM use for other precious stones diagnostics such as rubies, blue sapphires, emeralds and alexandrites and proof for some kinds of treatment.
The experts of the Gemological Laboratory in SGCU as well as the other gemologists throughout the world tried to expand the boundaries of the Diamond View TM device use on the matter of diagnostics of other mineralogical groups of stones, as well as methods of their treatment. Nowadays, the production of synthetic stones has increased significantly due to their lower cost, easy accessibility and high grading characteristics, but their determination may become a difficult task even for experienced gemologists. The results of our research illustrated with photo are represented below.
COMMON TREATMENT METHOD USED FOR DIAMOND IS FRACTURES FILLING WITH A COLORLESS HIGHLY REFRACTIVE SUBSTANCE TO ENHANCE CLARITY AND APPEARANCE OF THE STONE.
In order to make diamond defects less noticeable, a method of fractures and cavities filling with highly refractive substances (presumably molten glass, silicone oil, silicone-based mass) has been developed. The technologies for filling fractures in diamonds appeared in the 80s of the 20th century. A treated stone looks more attractive than the untreated one, so it became very popular soon. The main criteria to reveal this treatment method is the presence of “flash effect”, which is caused by the difference in reflection index of filler substance and the diamond. The Diamond View TM device easily helps to diagnose filler in the fractures. The filler becomes noticeable during the stone exposure under the ultraviolet light (Fig. 1).
DIAGNOSTICS OF NATURAL AND SYNTHETIC MINERALS OF THE CORUNDUM GROUP Gem-quality corundum stones growing became possible at the end of the 19th century and they are still popular in Ukrainian jewelry market. Experts of SGCU often deal with synthetic rubies and sapphires. To determine the origin of the corundum group stones, usually use gemological microscope and other laboratory equipment.
DIAGNOSTICS OF NATURAL AND SYNTHETIC RUBIES Diagnostics of the origin of raw rubies is an easy task due to the distinct crystal shapes of natural and synthetic stones (Fig. 2) After the lapidary, the task becomes more complicated because the main diagnostic criterion, the crystal shape, is no longer a characteristic feature of origin. Despite the Diamond View TM is an auxiliary tool for synthetic rubies determination, it gives very good results in determining synthetic rubies grown by Verneuil and hydrothermal methods. The typical growth structures appear during the short-wave UV-light exposure on natural rubies. The most common are structures along a hexagonal prism or their fragments. (Fig. 3B) During the Verneuil synthetic rubies study, besides the intense fluorescence, curved growth lines appear, which is reliable criterion of this synthesis method (Fig.4B). Presence of angular, narrow chevron-like structures are typical for rubies grown by the hydrothermal method (Fig.5B) and is an important diagnostic criterion for synthetic rubies grown by this method. Fractures filling treatment in natural rubies with a glasslike substance with a high Pb content is very common. Gas bubbles are observed (Fig.6A) during the glass-filled natural rubies study. The bubbles become more contrasting and the filler glows (Fig.6B) during the UV light exposure. Diagnostics of natural and synthetic sapphires Natural blue sapphires have the same characteristics as rubies, but the different color and intensity of fluorescence due to the presence of Fe, which replaces Cr in the crystal lattice. The growth structures appears in the form of fragments of hexahedral pyramids, which are typical crystallization form for sapphires (Fig. 8B). Very contrasting curved growth structures are typical for synthetic blue sapphires grown by the Verneuil method (Fig.9B), their appearance is a very reliable criterion for this synthesis method. Synthetic blue sapphires grown by the hydrothermal method also show typical signs for this synthesis method. Angular chevron-like growth structures become clearly visible under the UV light exposure and their appearance differs depending of the view: crown (Fig.10A) or pavilion (Fig.10B) There are similar criteria to those described earlier in rubies, namely, gas bubbles and thickening of color along the filled fractures in natural blue sapphires, treated by the fractures filling method with high Pb content glass-like substance (Fig.11A). The gas bubbles appear more contrasting and the filler becomes clearly visible under the UV light exposure (Fig.11B).
DIAGNOSTICS OF NATURAL AND SYNTHETIC EMERALDS
When studying the minerals of beryl group, namely emerald, since it is the most common and expensive variety on the jewelry market, well-shown growth structures along the hexagonal prism, which are typical for emerald (Fig. 13B) are not common. The stones without clear structures or with insignificant fragments of structures, with red fluorescence due to the presence of Cr in the crystal lattice are more common. Synthetic emeralds grown by the hydrothermal method show angular chevron-like structures. The structures are clearly seen even in visible light (Fig. 14A), and become more contrasting under the UV exposure (Fig. 14B). In the case when emerald is treated by the fracture filling method, the presence of the filler is clearly visible in UV light (Fig. 15).
DIAGNOSTICS OF NATURAL AND SYNTHETIC ALEXANDRITES
The authors observed weak or insignificant fluorescence and the absence or insignificant fragments of typical structures for the rhombic crystallization system during the alexandrites study. In some cases, there were specimens with full and obvious structures (Fig. 17B). Unconventional approach is highly recommended in the gemological practice in the issues of origin diagnostics as well as precious stones treatment marks revealing.Red fluorescence due to the presence of Cr and elongated gas bubbles are observed in synthetic alexandrites grown by the Czochralski method and they are reliable criteria for stones diagnostics grown by this method (Fig. 18) Synthetic alexandrites obtained by growing from a solution in a melt (flux method) have red fluorescence and elongated flux remnants as well as veils, which are observed in both visible and UV light and are diagnostics criteria for this method (Fig.19).
Unconventional approach is highly recommended in the gemological practice in the issues of origin diagnostics as well as precious stones treatment marks revealing. Even though Diamond View TM has been designed for a very specific task of diamond origin determination, it shew itself as a reliable assistant for a wider range of gemological tasks and this article is demonstrative evidence.