When meaning deposits of platinum were discovered in the Ural mountains, the russian authorities, and in detail the then Minister of Finance, Count Egor F. Kankrin wanted to use it for coinage along with amber and eloquent denominations. The value proportion between the three metals was set at 15.6:5.2:1 for amber, platinum and argent, respectively. large-scale platinum ore processing began following the decisiveness in April 1828 to issue platinum roubles. This was done at the Royal Mint in St. Petersburg, supervised by General Sobolevsky. A technically successful march used about 20 tonnes of platinum ore from 1828 to 1845, striking more than 1.3 million 3 ruble pieces ( Figure 1 ), about 15 thousand 6 ruble pieces and 3474 12 ruble pieces, with a entire platinum burden of 485,505 troy ounces ( approximately 15.1 tonnes ) ( Reference ( 4 ), page 247 ). The monetary side, however, was less successful. In 1845 the russian government demonetised the entire platinum neologism, which was sold to respective european platinum refineries for reworking .
Fig. 1
There was something of an ‘ afterlife ’ for the russian platinum roubles when the Russian Royal Mint produced fresh coins ( ‘ Novodels ’ ) for collectors in the late nineteenth century. Officially struck, using the original dies, these are numismatically identical to the original series. It may be difficult to distinguish authentic early to mid-19th century coins from the ‘ Novodels ’ by established numismatic criteria, particularly since the latter are typically in mint stipulate, and more likely to be found in major reference point collections. A written birthplace is much miss, so a scientific protocol is required to distinguish ‘ Novodel ’ issues from monetary coins. A foster complication is the universe of twentieth hundred forgeries, allegedly produced in the Lebanon, and possibly besides elsewhere. late literature ( 1–3, 9 ) has drawn attention to a valuable body of technical data. It is the aim of this paper to give an up-to-date, first-hand bill of key results from the ongoing inquiry of the author ‘s group into these coins, and to outline the electric potential of early coins and medals for providing lineal and precise information regarding the development of platinum metallurgy over more than a century .
Early 19th Century Platinum Refining
The early metallurgy of platinum was well hampered by its chemically and thermally fractious nature, and by the presence in the ore of early, not well dissociable elements ( typically about 25 % in entire of varying amounts of the early platinum group elements, plus iron and bull ). Most propose refine methods relied on dissolving the ore in greenish blue regia ( mix concentrated hydrochloric and azotic acids ), followed by selective precipitation of platinum as ammonium hexachloroplatinate. careful wash was needed to remove adenine much of any coprecipitated iridium and iron salts as possible without excessive loss of platinum. The dry precipitate was brought to red heat, driving off the ammonia water and chlorine, and yielding a metallic platinum sponge. The leech was then ground, forged and hammered, with repeated annealing cycles. The result was a solid alloy which was forged into bars and sheets. The concentration of the metal sponge increased increasingly during hammering to a utmost of around 21 gigabyte cm−3, close to that of saturated platinum at 21.45 guanine cm−3. Over twenty years, Wollaston perfected the refine and work of platinum at a lab scale to economic success ( 6 ). The Royal Mint in St. Petersburg, on the other hired hand, pioneered industrial use of the early powder metallurgy, reportedly with respective refining variants along the way ( 4, 7, 9, 10 ). The proportional merits and efficacy of the variants in terms of finished metallic element choice can not be judged from these publications alone .
Investigation of Russian Platinum Coins
Bachmann and Renner ‘s ( 11 ) were the first base analytic results, based on scanning electron microscopy and x ray fluorescence analysis on an 1829 3 ruble piece. There was a significant degree of porosity at the coat, as expected for material produced by powderize metallurgy, and with 0.5 wt. % cast-iron and about 0.1 wt. % each of palladium, rhodium and chromium present. The concentration of the material was 20.7 deoxyguanosine monophosphate cm−3. The authors record a visible improvement of the surface quality of the coins over the production menstruation. There has been no metallographic study, or discussion of the range and origins of impurities, until recently. The present study used a series of 3 ruble coins from 1828 to 1842. It was prompted by the observation of a magnetic here and now and deficient concentration for most of them. only the 1828 coin was in mint condition ; the early eight showed acquit signs of wear and circulation. A russian Olympic commemorative platinum mint struck in 1977 was included to represent more holocene metallurgical standards. analysis was largely non-sampling and non-destructive. lone one of the coins was sampled for metallographic study. Full analytic details and results have been published elsewhere ( 9, 12–14 and literature cited therein ). This newspaper summarises the results and addresses the coins ’ electric potential significance for the history of platinum metallurgy .
Material Characterisation
Metallographic Investigation
The 1837 coin was chosen for metallographic investigation of its inside, having shown the strongest magnetic reaction to the hand-held attraction and among the highest impurity contentedness in the XRF analysis. however, its calculated iron content according to XRD and eddy current readings was entirely moderate. Sampling was done with a slow-moving diamond-impregnated cutting wheel, removing a triangular cross-section from the flange. The sample was mounted in cold-setting resin, perpendicular to the coin ‘s compressed surfaces ; then flat coat and polished by standard procedures down to a quarter micron diamond finish for optical and scanning electron microscopy. Most fall upon under the ocular microscope was the high density of bantam oxide inclusions throughout the body of the mint, but notably absent immediately beneath the two independent surfaces ( Figures 2 ( a ) and 2 ( b ) ). The inclusions consisted chiefly of oxides of iron and nickel. Two distinct, adjacent oxide phases were observed, hematite and magnetite, which are described in Table III .
Fig. 2(a)
Fig. 2(b)
Table III
| Oxide inclusion, identified by Raman spectroscopy (12) | Colour | Composition, determined by electron micro-probe analysis |
|---|---|---|
| Haematite | Bluish, with intense red internal reflections | Pure iron oxide |
| Magnetite (iron-deficient) | Greyish | 5 wt.% nickel oxide |
The marked absence of metallic oxide inclusions near the surfaces, and within certain layers in the body, was interpreted as a result of pickle of the hammer sheet alloy during the process, before its being folded over for repeat hammer, and then of pickle of the coin blanks after the final annealing. This would have removed any oxide scale from the open and the immediate sub-surface layer. notably, there were no voids or pores in the consistency, nor were any grain boundaries apparent. however, in cross-section the outer surfaces did show some imperfections and irregularities ( for example, Figure 2 ( a ), top character of machine rim ), comparable to those observed earlier by Bachmann and Renner ( 11 ) using non-destructive SEM imaging The clean near-surface layers and the inclusion-rich body were analysed individually by a scanning electron microscope fitted with a wavelength-dispersive mass spectrometer. Results are summarised in Table IV. The iron results were the most interesting, showing a absolved tendency to higher concentrations in the body than near the surface. This promote corroborates the guess of partial derivative iron depletion of the surface metallic element by oxidation and leach .
Table IV
| Region | Average content, wt.%* | |||
|---|---|---|---|---|
| Fe | Ni | Ir | Rh | |
| Near-surface layers | 0.73 | 0.03 | 0.85 | 0.57 |
| Body of the coin | 1.40 | 0.05 | 1.06 | 0.51 |
To elucidate the metallographic structure of the platinum matrix, and to better understand the relationship of the inclusions to the matrix, we turned to the Johnson Matthey Technology Centre for help with etching. This was done in hydrochloric acerb saturated with sodium chloride, and applying an alternating stream to the sample. initially, the engrave attacked the oxide inclusions only. The metallic grain structure which finally became visible was relatively coarse, with a clear elongation of the person grains parallel to the directly surfaces of the coin ( Figures 3 ( a ) and 3 ( b-complex vitamin ) ). The cycles of forge and annealing, the latter frequently at high temperatures and over many hours ( 4 ), anterior to the strike of the coins, had clearly obliterated the initial structure of the alloy sponge. Grains were on average about two orders of magnitude larger than the inclusions. No systematic spatial relationship between the inclusions and the alloy grains was apparent .
Fig. 3(a)
Fig. 3(b)
Compositional Characterisation of the 1828 and 1977 Coins
together with the six coins dated between 1829 and 1842, two belated coins not intended for circulation were analysed by XRF : the ‘ Novodel ’ issue labelled 1828, but probably made in the late 19th or early twentieth hundred, and the 1977 commemorative issue. Their density and XRD pattern were much closer to the theoretical values for pure platinum ( see above ). They gave no unusual magnetic reply. Their chemical ( surface ) musical composition is given in the bottom two rows of Table II. It is obvious that they are made from more highly refined platinum, with much lower levels of all contaminants. not unexpectedly, the 1977 mint shows the least contaminations, with about 550 ppm iron as the major impurity, whereas the ‘ Novodel ’ offspring ( Figure 4 ) silent has more than 2000 ppm iridium and iron, and a slenderly higher copper message than the 1977 emergence. noteworthy is the about accomplished separation of gold, beginning witnessed here ( Figure 5 ) .
Fig. 4
Fig. 5
The occurrence of anomalously high levels of certain elements on one surface only is not restricted to the early coins ; the ‘ Novodel ’ issue has on its obverse much higher readings for titanium, iron and zinc. The origins of these and other like high readings are not however known, requiring more research on both fabrication and subsequent discussion .
Interpretation of the Results
The physical, chemical and metallurgical characteristics of the coins relate directly to their manufacture. The considerable contamination, both as discrete inclusion of cast-iron oxide, and as alloying elements in the platinum, such as cast-iron, iridium, copper, rhodium and gold, reflects the limitations of the complicate mathematical process based on selective precipitation from greenish blue regia. The practitioners of the time were well mindful of the necessity to rinse the hasty sufficiently to remove american samoa much of the iron as potential, but not so as to lose excessively much platinum. The methods available to separate iridium and platinum were all arduous and far from quantitative, so it is unsurprising that iron and iridium are the main contaminants in the coins, with concentrations of around 1 wt. % each. other elements, such as rhodium, palladium, copper and amber, company platinum into the precipitate to some extent. Iron was credibly the most deleterious contaminant, at higher concentrations rendering the metallic element excessively hard and brittle for successful invent and strickle. The upper specify of tolerability of iron contamination obviously depended powerfully on the intended use of the alloy, while the purity attainable depended on the skills and have of the practitioners angstrom much as on the quality of reagents and tools available. The research and development which finally made platinum feasible centred on mechanical treatment arsenic much as on the polish procedure ( 4 ). even Wollaston, the undisputed authority on refine and working platinum in the first decades of the nineteenth hundred, was not able to obtain platinum alloy barren of iron ; after each shape and annealing cycle he found iron scales which had to be removed by pickling before resuming the discussion ( 16 ). analysis of platinum wire made by Wollaston, and nowadays held in the Science Museum, London, found about 0.35 wt. % iron and 0.2 wt. % iridium ( 10 ). Metallographic probe of one of the coins demonstrated that the cast-iron is partially stage as iron oxide particles within the body of the coin, and partially as an alloying element in the platinum matrix. For telegram draw, both oxide inclusions and the hardening effect of the iron and iridium admixture component would have been damaging, requiring pure platinum than for mint mint. This observation is borne out in the different levels of residual contamination in the alloy of Wollaston ‘s wire and the russian coins. The academic degree of contamination in the eight genuine coins analysed hera falls in the range 2 to 4 wt. % of combine impurities near the airfoil ; there is a foster impurity contribution from the oxide inclusions within the mint matrix. The three coins with the lowest impurity levels are those minted in 1829, 1831 and 1835, that is, during the first one-half of the period of coin production. Iron, the element most critical to the malleability of refine platinum, shows no decrease during these years. iridium levels apparently increase slightly. This absence of a consistent course suggests that refining exercise remained basically largely unchanged, resulting in a platinum content of credibly only about 95 to 97 wt. % for the genuine coins. Looking at the datum reveals a convinced correlation coefficient in the concentrations of the three platinum group metals ( pgms ) : iridium, rhodium and palladium, with the highest measure for all three elements found in the 1842 coin, and broadly low values in the 1835 publish. Iron, on the other hand, follows a different pattern, reasonably well correlated with copper. This credibly reflects the different behavior of these elements during polish and fabrication ; we may assume that they all co-varied throughout the precipitation of the platinum sponge and the subsequent wash steps. lone copper and iron are likely to burn out as oxides during the hot invent and pickle. The nature of the oxide inclusions – hematite and oxidised magnetite – clearly indicates aggressively oxidize conditions during alloy serve. This is conducive to the foster removal of metallic iron from the debase during hot forge. It is known that the platinum ore was processed in batches of around 10 to 15 kg per day ( 8 ). One may assume that the note unevenness in mint typography reflects unevenness between batches rather than systematic changes in drill. On the other hand, Sobolevsky ( 8 ) mentions improvements in the refine procedure followed at the Royal Mint in St. Petersburg, so a reduction of overall impurity levels among the coins over the production period would thus not be unexpected. Schneider ( 17 ) reports that at some point the procedure to separate iridium from platinum changed from using an initial excess of hydrochloric acid in the solution, with selective precipitation of the platinum, to selective precipitation of all pgms other than platinum by adding limewater in dark. It is plausible that the generally higher and more ceaseless levels of iridium in the moment half of the production menstruation reflect this change. The quality achieved early on was obviously fit for the purpose, while the little increase in impurities over clock might even indicate that the mint masters learned to cope with them. however, to further explore the offspring of unevenness and trends in composition, a a lot more comprehensive series of analyses is required, covering multiple coins for each year, equally well as more archival research in Russia. A clearer distinction emerges between the genuine and the belated coins, which have sum impurity levels of less than one per cent ( board II, bottom two rows ). not unexpectedly, the 1977 mint shows the least contaminations, with about 550 ppm iron as the major impurity. In contrast, the 1828 ‘ Novodel ’ emergence hush has more than 2000 ppm each of iridium and iron, although most contaminants are stage in significantly lower concentrations than previously. The platinum content is better than 995/1000, if one ignores the possibly erratically high cast-iron content on the mint ‘s obverse. The ‘ Novodel ’ and 1977 issues demonstrate major build up in complicate and fabricate practices over more than a century, inaugural following the introduction of hydrogen-oxygen burners in 1847 and then, in the twentieth century, the introduction of electrochemical refine. The about complete separation of platinum and iridium, apparent from the 1977 coin, leaves iron as the last major impurity – present at more than equitable a couple of hundred ppm – therefore qualifying the platinum for “ 999 ” daintiness. The capacity of most impurities is below the detection limit for typical EDS systems attached to scanning electron microscopes, and iron levels alone are no reliable differentiator for genuine coins versus ‘ Novodel ’ issues. Willey and Pratt ( 3 ), for example, report identical humble levels of iron in their 1834 mint and use this to interpret this coin as a counterfeit. however, the EDS spectrum of that coin shows in addition to the iron flower a significant rhodium top out ( cystic fibrosis. their figure on foliate 137 of ( 3 ) ), strange in other ‘ Novodel ’ issues but appearing in other genuine coins ; besides, its weight unit is only 10.16 g, very much in production line with the actual coins studied here. This coin may have been made from a particularly iron-poor batch of metallic, but however within the period of genuine coin production. Lupton ( 2, p. 78 ) found flush lower iron levels in the two 3 ruble pieces analysed, of 0.3 and 0.4 wt. %, respectively ; these coins had densities of around 20.8 and 20.4 g cm−3 and sufficient other impurities to suggest that they were indeed genuine .
Conclusions
russian platinum coins have been analysed to characterise their physical and chemical properties. In junction with published information on the refine and exercise of platinum in general, and of these coins in particular, criteria have been established to distinguish authentic coins, issued between 1828 and 1845, from by and by official reissues, known as ‘ Novodels ’. The concentration of the authentic coins by and large falls between 20 and 21 g cm−3, while belated coins seem to have a density comfortably above 21 g cm−3. similarly, weights below the nominal 10.35 gravitational constant seem to be common among actual coins ( Table I ). A recognizable magnetism appears to be an indicator, though not a prerequisite, for authenticity, as is a complex form of specific chemical impurities in the metallic ( 14 ).
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A full understand of most of the watch physical and chemical characteristics of the nine coins studied hera was only possible through the metallographic probe of one of them ( the 1837 publish ). flush allowing that one sample distribution may be misleading, we feel that the metallography rendered much more reliable the interpretation of results obtained by non-sampling and non-destructive methods for all these coins. Platinum refine during the nineteenth century relied chiefly on a complex and then alone partially understand sequence of dissolution and precipitation. The independent criteria for the purposes of the Royal Mint in St. Petersburg were the malleability of the resulting alloy, to be balanced against the overall costs of the operation, and manageability at an industrial scale. The analysis of the genuine neologism of the first half of the hundred suggests that impurity levels were tolerable, peculiarly as regards iron and iridium. For both elements, typical concentrations were found to be in the one per penny range, distinctly worse than in Wollaston ‘s contemporary metallic element, refined at a lab scale ( 10 ). The relatively wide spread in impurity concentrations found among the coins analysed so far indicates a degree of flexibility in refine rehearse at St. Petersburg. The ‘ Novodel ’ issues are of a well higher purity than even the best genuine coins in terms of respective critical elements, including gold, iridium, copper, nickel and iron. The award analysis uses alone a one ‘ Novodel ’ topic, so quantitative word picture must be timid. A score increase in refining quality is, however, to be expected over the fifty years between the production of the original and the ‘ Novodel ’ issues, and apparent in all four major contaminants, iron, iridium, copper and amber. The russian 1977 issue, analysed as an exercise of a modern use of platinum for commemorative coins and medals, is about pure platinum, with merely infinitesimal transition metallic concentrations. It is identical obviously different from the nineteenth hundred metal. future work should concentrate on characterising the ‘ Novodel ’ issues more in full, both in their chemical composition and forcible properties such as magnetic response, density and possibly microstructure. This would greatly improve our discrimination between the two series, which are differently about indistinguishable. It would be of interest to study the homogeneity within and variability between individual metallic element batches of the genuine neologism on a year-to-year basis. This could show whether any of the indicate changes in St. Petersburg ‘s polish procedures resulted in systematic shifts in writing, if not in improvements in platinum fineness, or whether the observe variability of the composition just reflects the unevenness of ore batches or individual batch preparations, without a specific chronological swerve in quality .
