Weapon Arts are abilities which your weapons in Elden Ring can hold and, through them, you can become a more dangerous force in the Lands Between.
You can, however, replace a Weapon Art with an Ash of War ability through the use of the Whetstone Knife. Assigning the right Ash of War ability to the right weapon could be the change you need to take down a boss, so don't forget about them!
Below you'll learn where to find the Whetstone Knife and, once you have it, how to equip Ash of War abilities in Elden Ring.
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What are Weapon Arts in Elden Ring?
Weapon Arts are abilities a weapon can deploy, which you can execute by pressing L2 / LT. At a glance, you can see what the Weapon Art is via the text above your equipped items in the bottom left corner, as well as through the Equipment screen.
The vast majority of weapons will come with a Weapon Art, but can they be replaced with an Ash of War. Ashes of War can be found frequently in a variety of ways - as items in dungeons, rewards from bosses, or from specific vendors. Chances are as you'll explore, you'll accumulate a list of Ash of War abilities.
First, however, you will need a Whetstone Knife to equip Ash of War abilities.
Where to find the Whetstone Knife in Elden Ring
To get the Whetstone Knife at the start of the game, visit Gatefront Ruins. This is a location next to a huge gate north-west of your starting location in west Limgrave.
Once you have discovered the location, approach from the south-east. Here will be multiple sentries - it will be hard to sneak past or backstab them as they are clustered together, but initiating a battle shouldn't be too risky as it should only draw local enemies to your position.
The wolves can be tricky in a group, but go down easily if you take them down one at a time.
When the coast is clear, you should see an underground passage, tucked next to a low wall on the other side of the central path.
Take the stairs down and open the chest within for the Whetstone Knife. You'll also get Ash of War: Storm Stomp to add to your collection.
How to equip an Ash of War
To equip an Ash of War, once you have a Whetstone Knife, visit a Site of Grace. The option for Ashes of War should now be visible, and it's this menu where you can equip an Ash of War.
From here, you can select a weapon and assign an Ash of War. Not all Ashes of War will work for every weapon - but you'll see which are available as you select a weapon.
Once an Ash of War has been assigned to a weapon, it cannot be equipped to another without unequipping it first. The good side of this is Ashes of War are reusable - so if you want to use it on another weapon later, you can - once it's unequipped, of course.
Similarly, though the Ash of War will replace the Weapon Art inherent to the weapon it's assigned to, it will revert back to that once the Ash of War is unequipped.
In summary - Ashes of War are reusable, nor are Weapon Arts replaced for good. This allows you to experiment and try which Ashes of War work best for your weapons of choice.
Finally, though an Ash of War can only be used on one weapon at a time, you can acquire a second of that type for another weapon once you have found a Lost Ash of War and visited a Blacksmith.
A Blacksmith will be available in the Roundtable Hold, of which access becomes available in the Site of Grace just before the Margit fight. In other words - not long into the game at all.