Presenting the general properties and fascinating history of platinum.
Precious metals, known as noble metals, have amazing origin stories. Indeed, everything
from helium to iron is forged in the hearts of stars. These elements are the products of
fusion reactions, essentially. Well precious metals go one better, and the platinum group
takes it to another level.
The alchemist’s dream of transforming matter is just a matter of existing; if stars exist, matter transformation is happening. Fusion turns hydrogen into helium as if it was the most natural thing in the universe. In fact, it is. One moment, hydrogen is going about its business as it has since the Big Bang, and then gravity invites it to a party and it meets a nice neutron (or two) and transforms into helium. Well, the poetic licence there is our own, and no one approved it. Please send your brickbats my way. Essentially though, that is how fusion works (minus a proper explanation of the strong force) but its transformative powers do not go past iron.
Hydrogen and helium are the most abundant materials in the observable universe, and are primordial. They are also amongst the least massive (i.e. lightest for shorthand) elements on the periodic table. Although helium can be produced through fusion, as mentioned, and radioactive decay (we will not go there), this kind of transformation has its limits. For heavier elements, something more violently powerful than the fusion heart of even the most massive star is required. Even if such a star were to explode and spew its innards across the universe, this matter would not include platinum. There is simply not enough energy in even the most impressive supernovae we know of that can accomplish this. It is in fact something so rare that we have only recently observed it, although everything we know about cosmology suggested the possibility.
Used very sparingly in watchmaking, palladium is — like the other metals in these sidebars — a platinum group metal. In the periodic table, it is known by the symbol Pd, and its atomic number is 46. Palladium shares many of the same properties of platinum, including density and malleability. In fact, it is the least dense of the metals in its group and its melting point is the least extreme, although still high. It also shares the same catalytic properties that make it as appealing as platinum to industry, and it was the most cost-effective. In the recent past, palladium ore prices have outpaced platinum, in turn putting pressure on platinum ore prices. Besides the problematic issue of most supply coming from Russia, important mines there had already been hit by environmental issues.
As a result, palladium is estimated by some sources (Statista) to be 15 times as rare as platinum, which itself is just about as rare as gold. Since 2016, the price of palladium (per gramme) has increased fourfold; obviously, the effects of Covid-19 and the current conflict in Ukraine have not been factored in yet. On the other hand, there is no good reason to use palladium for watches, since it is very similar to platinum but does not have the cachet of that precious metal. At the same time, it might also be a good deal more dear than platinum, because of industrial demand and various supply constraints.
Among Swiss watchmakers, Cartier, Ulysse Nardin, Audemars Piguet and H. Moser & Cie have used palladium in recent years. Interestingly, the bulk metallic glass (BMG) of the Royal Oak Jumbo Extra-Thin 15202XT for the most recent edition of OnlyWatch featured palladium in the mix.
For this, we turn to pop culture, the excellent “Neutron Star Collision” by Muse. First, astrophysicists theorised that such things as neutron stars must exist — these are stellar objects composed entirely of neutrons. All the protons and electrons have fused into neutrons, in the wake of a particularly glorious supernova. If the object had just a little bit more mass to go on, it would collapse into a black hole. But it does not, and thus remains a mass of tightly packed neutrons. Cosmologists speculated that perhaps the extra mass (and therefore energy) needed to transform into a black hole could come from another such object, in the event of a collision. One result of such cosmic fireworks would be the production of heavy elements, like the platinum group of metals. Another possible explanation is the hypernova, which is basically a supernova on steroids, where a stellar object with sufficient mass sheds its outer layers as it collapses to form a black hole. In any case, the consensus appears to be that less dense precious metals such as gold can be produced in mere supernovas.
From these intense origins, platinum eventually settles into the crusts of planets like ours. Similar to gold and other dense metals, most of it probably sank right down to the core of the planet in question. Only a small part — approximately 5 μg/kg — is accessible in the crust, and approximately several hundred tonnes (Quill and Pad’s Joshua Munchow cites 150 tonnes, and precious metal traders generally put the figure at no more than 200 tonnes) are mined annually. Interestingly, as far as available sources go, platinum is about as rare as gold, but it is more difficult to extract. Fratello estimates that to get 30 grammes of pure platinum, 10 tonnes of raw platinum ore are required. That sounds incredible, and the website did not cite a source, but the short of it is that it is tough to get pure platinum to work with. The nature of the metal also makes it harder to recycle than gold, but this fact fits in better a little later in this piece.
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Rarity alone cannot account for any metal’s use in watchmaking (or jewellery for that matter). The properties of the metal must be suitable too. For example, iridium is in the same family of metals as platinum, but it is extraordinarily brittle, making it a challenge to machine. Similarly, rhodium is even rarer than platinum or gold, and commands astronomical prices on the commodities market. It also has an extremely high melting point and is not malleable — indeed it is often alloyed with platinum to give this material better rigidity — but more on rhodium below.
This Is Hardcore
Platinum, on the other hand, is extraordinarily malleable but also much denser than gold. To be perfectly clear here, pure platinum is harder than pure gold; it is approximately twice as hard in fact. While you can leave marks in gold by biting it, as movies sometimes demonstrate, you cannot do the same with platinum. Having said this, alloys change things, and there is a big difference in how gold and platinum are alloyed in watchmaking. For the moment, it is sufficient to know that 18k gold is just about as hard as 950 platinum, but the introduction already summarises most of the relevant information as it relates to Swiss watchmaking.
A contender for the world’s most expensive metal, averaging US$21,000+ per ounce in May this year, rhodium finds itself all over the place in watchmaking, but never as a full case material. It goes by the symbol Rh on the periodic table of elements, and its atomic number is 45. Unlike platinum and palladium, it is a group 9 element. It has the distinction of rarely ever being used to make complete structures, instead being typically encountered as a coating or plating. Hence, most people familiar with white gold will recall hearing about rhodiumised white gold, or rhodium-plated white gold. Compared with gold and platinum, no significant reserves of rhodium exist, and only some 20 tonnes are mined every year — making it a full order of magnitude lower than platinum. Given that rhodium is in the same noble metals group as platinum and palladium, it is unsurprising to learn that it too is an important catalyst. Unlike the other metals, rhodium’s primary purpose in catalytic converters is to restrict nitric oxide emissions in exhaust fumes; rhodium is the only element that manages this neat trick so there are no viable alternatives for it.
We also learned, from Periodic Videos, that rhodium is used as a complete structure to filter out harmful x-rays in diagnostic tools used to detect cancer. All this goes a long way to explaining why rhodium is both special and rare — and why you will not encounter it as a full object in watches and jewellery. However, rhodium’s corrosion-resistant properties are also a useful protection against corrosion (think silver and brass) and this is how most of us will have made its acquaintance. Ebauches are regularly given rhodium plating (one micron thick or so) to ensure better durability, and EuropaStar reports that as the primary role of this most precious of metals. Rhodium is also the second brightest of all metals (after silver) so it does have important aesthetic properties too. This makes it useful on appliques on dials, for example, while it also makes dull old white gold a bit more exciting.
To close this section, here are the basics on platinum. Its atomic number is 78 and it is listed in the periodic table of elements as Pt (also how it is denoted on watch cases). It is part of the group 10 chemical elements in the periodic table, alongside nickel and palladium (and possibly one other uncharacterised element), while also being the core constituent of what we call the platinum group of metals, alongside palladium, rhodium, ruthenium, iridium and osmium. These other metals will mostly be familiar to watch buyers, enthusiasts and hobbyists, and we include sidebars here for the ones most widely used in watchmaking.
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