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On the probability-based approach to identifying the origin of polished diamonds

20 february 2024

The sanctions imposed by the G7 countries on the Russian-origin diamonds should inevitably have led to efforts aimed at developing hardware and software systems allowing the identification of the origin of polished diamonds to create appropriate customs barriers. During 2023, several news and reports about such developments appeared in the diamond industry publications, the most striking of which was the advertisement of a certain device offered by the Spacecode company that supposedly allowed the determination of a diamond deposit (and, accordingly, the country of origin) where any polished diamond originated from based on its properties, which was considered impossible earlier. Specific details of the technology were not disclosed. Industrial production of the wonderful machine was planned for the end of 2023, but, as far as we know, such equipment has not yet been declared at the G7 countries’ customs.

In contrast to the Spacecode’s advertisements, more meaningful data on the problem under consideration was reported at the 13th All-Russian Scientific and Practical Conference held in March 2003 and dedicated to the geology and mineral resources of the North-Eastern regions of Russia. The report “Statistical Analysis of Data on the Impurity Composition of Rough Diamonds and Polished Diamonds Manufactured from Them” by the researchers of the North-Eastern Federal University (Yakutsk) describes a technique that, at first glance, is quite suitable for solving the problem of identifying the origin of polished diamonds1.

This work was done as follows. The authors selected 60 rough diamonds from the International and Yubileynaya (Jubilee) kimberlite pipes, as well as from the Molodo placer deposit (20 stones from each deposit). All gemstones were high jewelry quality rough diamonds weighing from 0.45 to 0.65 carats. The certain crystals’ impurity and imperfection profile (impurities of types H, B2, N3, P1, 490.7, N3V) was determined by the infrared, ultraviolet and Raman spectroscopy and the electron paramagnetic resonance method. Then, these rough diamonds were cut and polished and the data on the impurities in the polished diamonds manufactured from them was obtained using the same methods. Next, an analysis was carried out to determine a correlation ratio between the samples’ impurity and imperfection profiles in the initial state of the rough diamonds and that after cutting and polishing them, and the correlation in the crystal impurities and imperfections of the studied samples was determined. A regression analysis was carried out and regression coefficients were obtained for all three deposits calculated as the ratio of the particular imperfection concentration in the polished diamond to the imperfection concentration in the original rough diamond. The authors come to the conclusion: “Using regression coefficients, it is possible to calculate - based on the measured imperfection concentrations in polished diamonds - the imperfection concentrations in the original rough diamonds, and to correlate them with the data on the deposits to determine - with a relatively high degree of probability - the source of origin of the rough diamonds from which the polished diamonds are made.” The authors also determined the minimum sample size of polished diamonds required to identify the source of origin at a confidence level of 95%, which is 384 samples from one deposit.

In our opinion, the proposed method is not contradictory and, in principle, can serve as the basis for a hardware-software complex that allows to identify the origin of a polished diamond by its spectral ‘pattern’ with a certain probability. Based on a number of signs, it is possible to come to the conclusion that similar ideas were used in the widely advertised Spacecode’s equipment, although this company is unwilling to give details. It would seem that all that remains is to take appropriate samples from known deposits, make catalogs of spectral ‘patterns’ of reference rough diamonds and polished diamonds manufactured from them, make correlation matrices, calculate regression coefficients, upload all this data into the software and voilà - any customs officer can put your polished diamond in a loud buzzing box and immediately find out that, most probably, it was manufactured from a rough diamond mined, for example, at the International or the Jubilee pipes in Russia, meaning this polished diamond cannot be imported into the G7 countries. With proper funding, the necessary databases for the operation of such equipment can be created within a rather short time. So, is the triumph of those who fight the ‘Russian blood diamonds’ already close? Let’s not jump to conclusions, there are at least two significant obstacles to the implementation of such a wonderful idea.

The first obstacle is that no spectral analysis methods can answer the questions “When was the rough diamond under study mined?” and “When was the polished diamond under study cut and polished?” Unlike many luxury items, polished diamonds do not show signs of age. And the customs officer’s claims to a ‘Russian-origin diamond’ will inevitably face the absolutely fair statement that a rough diamond is indeed of Russian origin, but it was mined or cut and polished 1, or 3, or 10, or more years before sanctions were imposed, and, therefore, should be considered an absolutely legitimate item. As proof, a polished diamond owner can provide identification documents that are not much more difficult to produce than a notorious Kimberley Process certificate. By the time the G7 countries imposed their sanctions, hundreds of millions of carats of Russian-origin rough and polished diamonds - not included in any blockchain - moved through the diamond pipeline, and hundreds of millions of carats of polished diamonds made from the Russian-origin rough diamonds mined and exported from 1946 to 2023 circulated on the secondary market. So, should all these polished diamonds be deemed illegitimate now? Perhaps, there should be a penalty for owning and trading in these diamonds, or at least some additional tax to be paid by diamond owners? It is clear that this paradox cannot be resolved by taking a common-sense approach, but since the sanctions have long gone beyond this approach, one can expect a total ban on importing the Russian-origin rough and polished diamonds into the G7 countries, regardless of the production date.

Then, a second obstacle appears that is not taken into account, at least for now, by the authors of methods for identifying the origin of rough and polished diamonds and by potential customers of hardware and software systems built on these methods. The fact is that all these methods are probability-based in nature. The origin of a polished diamond can be determined with a ‘high probability’. In fact, it is proposed to make a legal binary decision (of course, a ban or permission to import is a legal decision) after an expert examination that is based on probability.

But the problem of the possible use of the probability-based expert opinion as evidence when making legal decisions has been discussed for a long time and, in practice, is resolved in different ways depending on national standards for expert reports. In the USSR, for example, an expert report with a probability-based conclusion could not be accepted as evidence in court, and this tradition is partly maintained in modern Russia. In Germany, on the contrary, formulating a probability-based conclusion is encouraged in expert practice, and the acceptability of probability-based expert evaluations varies greatly from country to country. Any customs restrictions and bans are inevitably fraught with litigation at law. Since the judicial practice of the G7 countries has significant differences in assessing the probability-based approach to making expert evaluations, the implementation of hardware and software probability-based systems for identifying the origin of polished diamonds should be agreed upon at the level of national legislation, which poses a problem almost more complex than developing these systems.

Identification methods and equipment should be described in great detail in the open publications, and the criteria and the threshold probability values allowing to attribute the polished diamond under study to a specific deposit should be perfectly justified. And the entire procedure should be aligned with national standards of judicial evidence, which will be quite difficult given the differences, for example, between the French and the Japanese standards. The task is very challenging and labor-intensive, and it is unlikely to be solved this year.

Sergey Goryainov for Rough&Polished

1 Ivanov M., Leontiev S., Fedotova M., Everstova D. Statistical Analysis of Data on the Impurity Composition of Rough Diamonds and Polished Diamonds Manufactured from Them. Geology and mineral resources of the North-East of Russia: materials of the 13th All-Russian scientific and practical conference with international participation / Editor-in-Chief V. Yu. Fridovsky. – Yakutsk: NEFU Publishing House, 2023, pp. 88 – 91.