Yes, it is possible. But you probably wouldn’t want to.
Let us explain.
Can You Melt Obsidian and Cast a Sword? (EXPLAINED)
Leave it to Hollywood to create possibilities with pure fiction.
In the hit cable HBO TV series, Game of Thrones, the bad ice demon people were killable using the equivalent of an obsidian sword, except in the show it was called dragon-glass.
While obsidian is extremely sharp, it has historically been used as a blade such as a dagger.
While it can be shaped, melting it would take significant resources, and it would never function as a practical sword.
That said, people still try silly things.
Why Obsidian is So Brittle
As a material, obsidian is essentially a melted silicon mixture, i.e. sand.
It is made up of about 70 percent silicon dioxide as well as a lot of contaminants from aluminum oxide and anything else that got picked up during the volcanic creation process.
The heat point at which obsidian starts to melt and become liquid form is intense and considerable.
While this is not a problem inside a volcano, man-made melting conditions would need to reach at least 1,710 degrees Fahrenheit for the silicon part of the obsidian and 2,072 for pure liquification of everything else in the mix.
Most facilities simply don’t have the tooling to handle that kind of temperature.
Naturally, obsidian cools over a period of time when it forms into is glass-like state.
In an artificial setting, the typical cooling process involves quenching of metal.
That doesn’t work for obsidian.
A sudden shock of cooling would shatter the obsidian and produce lots of fragments instead of a solid cast.
Instead, it would need to be air-cooled, similar to what one does when forming a glass bottle.
Cooling Would be a Nightmare
In terms of the actual casting into a sword form, assuming one had the tooling and means to cool the melted obsidian down into the new form, the end product would be a very brittle sword form that was easily breakable just from trying to pull it out of the cast.
Again, obsidian is essentially a rock form of glass.
Without any kind of internal structure to strengthen it, obsidian tends to be highly malleable to impact and shock, showing ripple waves going through it during impact and fracturing almost immediately.
So, as an impact weapon, what would be produced would be completely useless.
Obsidian’s one key advantage as a sword of any form is its sharpness on soft, organic material.
It is possible to make stronger forms with other types of glass that are similar to obsidian in appearance and look.
Because these materials have more impurities in them, they could look, act and feel stronger, but again, being glass, they would still be easily breakable.
An Incredible Cutting Edge
The function of obsidian as a weapon comes from its natural edge and sharding when broken off from bigger pieces.
Obsidian has a microscopic edge that cuts extremely clean, especially through organic materials like meat, plant, leather and similar.
The edge is so small, some in the scientific community argue it could actually split down to the atomic level.
There is no question the glass tone can cleanly cut at the cellular level.
This has been proven with microscopic photography.
Comparative cuts with metal look like someone took a chainsaw to things versus a scalpel.
And the cuts can be very sharp and fast when applied in a slashing or stabbing form.
So, obsidian could have a use as a weapon, more in the form of a cutter or dagger as opposed to a sword.
Obsidian has Been Used for Centuries
Historically, obsidian dates back to early human activity as one of the earliest cutting tools.
However, all of these tools were produced through sharding and scavenging versus anything involving melting.
Naturally, obsidian can be found in former volcanic areas and becomes visible when it gets exposed to the surface ground level or through mining.
It can also be found in the form of “lava bombs,” globs of lava hurled from the volcano that cooled off into round rock form but when cracked open are obsidian inside.
Early humans found bits and pieces of obsidian all the time, and they realized the shards were extremely useful for cutting small things and scraping.
The brittleness of obsidian also made it shapeable by chipping.
Early people used everything from other stone to bone to shape small bits of obsidian into spear points, smaller cutters, needles and even arrowheads.
It wasn’t until brass, iron and then steel came along that better finesse was possible, replacing obsidian entirely.
Later humans did find use for obsidian in other weapons though.
Mesoamerican cultures often lived near volcanoes and found the rock frequently.
They utilized it as mentioned above as well as combining it with wood to make more powerful tools and weapons.
A common Mesoamerican weapon with obsidian was the Macuahuitl.
This club-like stick involved a solid trunk and flat wood center with obsidian shards on the edge to create added damage to a target when it was hit.
The obsidian itself would likely break in the impact, but the glass bits would cause a lot of damage during the hit on skin and leather, basically what people wore at the time before the Spaniards arrived in Central America.
The more fragments snapped off, the more dangerous the club became during conflict.
So, the last person hit probably suffered the most from multiple lacerations and contusions.
No Practical Weapon Application in Modern Times
Today, obsidian has no use as any kind of a weapon as steel and other forms of stronger metal work far better.
However, the glass rock is very useful as an experimental medical tool in surgery, producing extremely fine cuts that heal faster with far less scarring.
Unfortunately, the brittleness of the glass means one has to be very skilled in the use of such specialized tools, or fragments could break off and be left inside a patient.
So, while the evil ice demons of Westeros can be vanquished easily with obsidian swords, in the real world the glass rock is anything but a perfect weapon resource.
For giggles and a lot of hard work, one could melt the rock and form something that looks like a sword, but it would not be functional.
And, it’s probably far easier and faster to form a small sword by sharding a piece off a big rock of obsidian instead and flint-knapping it, the way humans formed obsidian tools centuries earlier.