Because of the volatility and extreme toxicity of its oxide, osmium is rarely used in its pure state, but is instead often alloyed with other metals for high-wear applications.
Osmium alloys such as osmiridium are very hard and, along with other platinum-group metals, are used in the tips of fountain pens, instrument pivots, and electrical contacts, as they can resist wear from frequent operation.
They were also used for the tips of phonograph styli during the late 78 rpm and early "LP" and "45" record era, circa 1945 to 1955.
Osmium-alloy tips were significantly more durable than steel and chromium needle points, but wore out far more rapidly than competing, and costlier, sapphire and diamond tips, so they were discontinued.

Osmium tetroxide has been used in fingerprint detection and in staining fatty tissue for optical and electron microscopy.
As a strong oxidant, it cross-links lipids mainly by reacting with unsaturated carbon–carbon bonds and thereby both fixes biological membranes in place in tissue samples and simultaneously stains them.
Because osmium atoms are extremely electron-dense, osmium staining greatly enhances image contrast in transmission electron microscopy (TEM) studies of biological materials.
Those carbon materials otherwise have very weak TEM contrast (see image).
Another osmium compound, osmium ferricyanide (OsFeCN), exhibits similar fixing and staining action.

The tetroxide and its derivative potassium osmate are important oxidants in organic synthesis.
For the Sharpless asymmetric dihydroxylation, which uses osmate for the conversion of a double bond into a vicinal diol, Karl Barry Sharpless was awarded the Nobel Prize in Chemistry in 2001.
OsO₄ is very expensive for this use, so KMnO₄ is often used instead, even though the yields are less for this cheaper chemical reagent.

In 1898 an Austrian chemist Auer von Welsbach developed the Oslamp with a filament made of osmium, which he introduced commercially in 1902.
After only a few years, osmium was replaced by the more stable metal tungsten.
Tungsten has the highest melting point among all metals, and its use in light bulbs increases the luminous efficacy and life of incandescent lamps.

The light bulb manufacturer Osram (founded in 1906, when three German companies, Auer-Gesellschaft, AEG and Siemens & Halske, combined their lamp production facilities) derived its name from the elements of osmium and Wolfram (the latter is German for tungsten).

Like palladium, powdered osmium effectively absorbs hydrogen atoms.
This could make osmium a potential candidate for a metal-hydride battery electrode.
However, osmium is expensive and would react with potassium hydroxide, the most common battery electrolyte.

Osmium has high reflectivity in the ultraviolet range of the electromagnetic spectrum; for example, at 600 Å osmium has a reflectivity twice that of gold.
This high reflectivity is desirable in space-based UV spectrometers, which have reduced mirror sizes due to space limitations.
Osmium-coated mirrors were flown in several space missions aboard the Space Shuttle, but it soon became clear that the oxygen radicals in the low Earth orbit are abundant enough to significantly deteriorate the osmium layer.

The only known clinical use of osmium is synovectomy in arthritic patients in Scandinavia.
It involves the local administration of osmium tetroxide (OsO₄), which is a highly toxic compound.
The lack of reports of long-term side effects suggest that osmium itself can be biocompatible, though this depends on the osmium compound administered.
In 2011, osmium(VI) and osmium(II) compounds were reported to show anticancer activity in vivo, it indicated a promising future for using osmium compounds as anticancer drugs.
Because of the volatility and extreme toxicity of its oxide, osmium is rarely used in its pure state, but is instead often alloyed with other metals for high-wear applications. Osmium alloys such as osmiridium are very hard and, along with other platinum-group metals, are used in the tips of fountain pens, instrument pivots, and electrical contacts, as they can resist wear from frequent operation. They were also used for the tips of phonograph styli during the late 78 rpm and early "LP" and "45" record era, circa 1945 to 1955. Osmium-alloy tips were significantly more durable than steel and chromium needle points, but wore out far more rapidly than competing, and costlier, sapphire and diamond tips, so they were discontinued.
Osmium tetroxide has been used in fingerprint detection and in staining fatty tissue for optical and electron microscopy. As a strong oxidant, it cross-links lipids mainly by reacting with unsaturated carbon–carbon bonds and thereby both fixes biological membranes in place in tissue samples and simultaneously stains them. Because osmium atoms are extremely electron-dense, osmium staining greatly enhances image contrast in transmission electron microscopy (TEM) studies of biological materials. Those carbon materials otherwise have very weak TEM contrast (see image). Another osmium compound, osmium ferricyanide (OsFeCN), exhibits similar fixing and staining action.
The tetroxide and its derivative potassium osmate are important oxidants in organic synthesis. For the Sharpless asymmetric dihydroxylation, which uses osmate for the conversion of a double bond into a vicinal diol, Karl Barry Sharpless was awarded the Nobel Prize in Chemistry in 2001. OsO₄ is very expensive for this use, so KMnO₄ is often used instead, even though the yields are less for this cheaper chemical reagent.
In 1898 an Austrian chemist Auer von Welsbach developed the Oslamp with a filament made of osmium, which he introduced commercially in 1902. After only a few years, osmium was replaced by the more stable metal tungsten. Tungsten has the highest melting point among all metals, and its use in light bulbs increases the luminous efficacy and life of incandescent lamps.
The light bulb manufacturer Osram (founded in 1906, when three German companies, Auer-Gesellschaft, AEG and Siemens & Halske, combined their lamp production facilities) derived its name from the elements of osmium and Wolfram (the latter is German for tungsten).
Like palladium, powdered osmium effectively absorbs hydrogen atoms. This could make osmium a potential candidate for a metal-hydride battery electrode. However, osmium is expensive and would react with potassium hydroxide, the most common battery electrolyte.
Osmium has high reflectivity in the ultraviolet range of the electromagnetic spectrum; for example, at 600 Å osmium has a reflectivity twice that of gold. This high reflectivity is desirable in space-based UV spectrometers, which have reduced mirror sizes due to space limitations. Osmium-coated mirrors were flown in several space missions aboard the Space Shuttle, but it soon became clear that the oxygen radicals in the low Earth orbit are abundant enough to significantly deteriorate the osmium layer.
The only known clinical use of osmium is synovectomy in arthritic patients in Scandinavia. It involves the local administration of osmium tetroxide (OsO₄), which is a highly toxic compound. The lack of reports of long-term side effects suggest that osmium itself can be biocompatible, though this depends on the osmium compound administered. In 2011, osmium(VI) and osmium(II) compounds were reported to show anticancer activity in vivo, it indicated a promising future for using osmium compounds as anticancer drugs.
Osmium