Osmiridium
A natural alloy of osmium and iridium, denser than anything else that occurs in nature — and once the tip of every good fountain pen.
Osmiridium is a naturally occurring alloy of the two densest elements there are, found as small hard grains in the same placer deposits as platinum. Like electrum it is a natural alloy rather than a manufactured one, and its composition varies with where it came from.
It is extraordinarily resistant to wear and to chemical attack, and extraordinarily hard to work — which fixed its uses for a century as a tiny amount of material at the point of something that had to last.
History
The fountain pen is the use it is remembered for. A gold nib is soft and would wear away in months, so a grain of osmiridium was welded to the tip; the trade still calls the tipping material iridium whatever it is actually made of. Phonograph styli, compass bearings and the pivots of precision instruments used it for the same reason.
It matters now mainly as a source. Osmium and iridium are both won from platinum-group concentrate, and osmiridium grains in placer gravels were how both elements were first isolated — Smithson Tennant found them in 1803 in the black residue left when crude platinum was dissolved in aqua regia.
How we know: checked recently · only one source, so there is nothing to cross-check it against · stated directly by the source.
How this connects
Where a connection has been confirmed by an outside reference, that reference is named beside it.
is composed of
- Osmium — element · 20–80% · one of the two densest elements known, and half of what makes the grains so resistant to wear
- Iridium — element · 20–80% · the other, in whatever ratio the deposit happened to deliver — it is a natural alloy, not a specification
- Platinum — element · a few per cent, from the placer gravels the grains are recovered from
is sourced from
- Platinum — element · recovered from platinum-group concentrate and from the placer deposits platinum itself is panned from — not manufactured
is an alternative to
- Tungsten carbide — compound · as a wear-resistant tip. Carbide replaced it almost everywhere on cost, and osmiridium keeps the places where chemical inertness matters as much as hardness
Sources
- Wikimedia Foundation · Creative Commons CC0 1.0 Universal (public domain dedication)
- Material WorldOur own writing